State tax docs / States / Connecticut
Connecticut state income tax: engine rules, 2026
How the QuantCalc engine computes Connecticut tax for tax year 2026, rule by rule, with the official source for each rule. Verification status: Worksheet-tested (what this means).
On this page: How the tax is computed · Rate schedule · Deductions, exemptions and credits · Social Security · IRA, 401(k) and private pensions · Public pensions · Military retirement pay · Roth conversions · Capital gains · Surtaxes and recapture · Part-year and nonresident returns · Worked examples · After 2026 · Not calculated ·
Verification. Machine-readable: this state's entry in the
engine config and the provenance file
(key CT).
How the tax is computed
Every step the engine takes for Connecticut, in the order it takes them. Steps marked with a filing status or household type apply only there. Each step links the section below that carries Connecticut's figures and the official sources for it; the calculation order page describes every step for all jurisdictions.
What each filing status gets, read back from the engine for a household with $1 of income (so below every phase-out and income test):
| Single | Married filing jointly | Married filing separately | Head of household | |
|---|---|---|---|---|
| Rate schedule used | single schedule | joint schedule | joint schedule, thresholds halved | head-of-household schedule |
| Top rate | 6.99% from $500,000 | 6.99% from $1,000,000 | 6.99% from $500,000 | 6.99% from $800,000 |
| Personal exemption (no standard deduction), under 65 | $15,000 | $24,000 | $12,000 | $19,000 |
| Personal exemption at 70 (joint: both 70) | $15,000 | $24,000 | $12,000 | $19,000 |
| Other personal exemption | none | none | none | none |
| Age subtractions at 70 (joint: both 70) | none | none | none | none |
- Per-person mode joint returns with the spouse's age given On a joint return with the spouse's age given, every age test the state applies per taxpayer is evaluated for each spouse at their own age. Without it one household age applies to both.
engine step (compute_state_tax_detail). Engine convention, no external source: The engine cannot know the second spouse's age unless told. - Blindness and disability, per person only when the caller says a person is blind or disabled The filer is person one; the spouse counts only on a joint return and only when the caller says so (there is no household convention as for age). Where a state lets a disabled person (and, where it says so, a blind one, or one whose spouse is disabled) qualify for its general retirement exclusion before the age, that person is treated as having reached the age for that exclusion only. Of the 42 taxing jurisdictions, these have a blind amount: Arizona, Arkansas, California, Colorado, Delaware, the District of Columbia, Hawaii, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Maine, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Missouri, Montana, Nebraska, New Jersey, New Mexico, North Dakota, Oklahoma, Oregon, Utah, Vermont and Virginia; these have none: Alabama, Connecticut, Georgia, Louisiana, New York, North Carolina, Ohio, Pennsylvania, Rhode Island, South Carolina, West Virginia and Wisconsin. A disability route is calculated in Arkansas, the District of Columbia, Georgia, Hawaii, Idaho, Iowa, Maryland, Michigan, New Jersey, Oregon and West Virginia.
engine step (compute_state_tax_detail). Engine convention, no external source: Who is blind or disabled is the caller's statement; the engine has no household convention for it. - Rate schedule and standard deduction by filing status Single uses the single schedule and deduction; married filing jointly the joint ones. Head of household and married filing separately follow the two steps below.
Connecticut's values · engine step (select_brackets). Sources (Rate schedule): 2025 Form CT-1040 TCS, Tax Calculation Schedule (checked 2026-09-27) - Married filing separately Where the state publishes its own separate schedule, that one (with half the joint deduction unless a separate deduction is set). Where one schedule applies to every status, that schedule unscaled with the single deduction. Otherwise the joint schedule with every threshold and the deduction halved (computed as the joint tax on twice the income, halved).
Connecticut's values · engine step (select_brackets). Sources (Rate schedule): 2025 Form CT-1040 TCS, Tax Calculation Schedule (checked 2026-09-27) - Head of household The state's head-of-household schedule where it has one, else the single schedule; the head-of-household deduction where set, else the single deduction.
Connecticut's values · engine step (select_brackets). Sources (Rate schedule): 2025 Form CT-1040 TCS, Tax Calculation Schedule (checked 2026-09-27) - The income total every income test uses Other ordinary income + retirement distributions (before any exclusion) + conversion + federally taxable Social Security + long-term gains + Railroad Retirement Tier 2. It stands in for federal adjusted gross income in every threshold, cliff and phase-out below; state subtractions do not reduce it.
engine step (compute_state_tax_detail). Engine convention, no external source: The inputs are the federal AGI components, so their sum is federal AGI for these income types. - Attributing income to each spouse joint returns with each spouse's own amounts given With a caller's split (the API's
spouseobject), each spouse's own distributions (employer-plan money included), pension, public pension, conversion, wages and military pay; spouse 2's shares are clamped into the household totals and spouse 1 gets the rest. Without a split, in per-person mode, every item is divided 50/50. Social Security is divided by each spouse's own gross benefits where the caller givesspouse.socialSecurityGross, else 50/50; other ordinary income and gains are always divided 50/50 where a rule needs a per-person amount. The split is used only where a state's rule is per taxpayer; household totals stay authoritative for the base and the income tests.
engine step (compute_state_tax_detail). Engine convention, no external source: Equal attribution is the neutral split when the owner of a dollar is not known. - The plan's minimum retirement age only when the caller gives the person facts (a civil service annuity, disability pay, Social Security disability, survivor benefits, an IRA basis or an exception) Where the state reads it, the minimum retirement age of the plan paying a person's disability pay (the filer's, or the spouse's on a joint return), when given: from that age the pay is a pension. Not given, each state keeps its own reading.
Connecticut's values · engine step (dis_plan_age). Sources (IRA, 401(k) and private pensions): 2025 Form CT-1040 Instructions (checked 2026-10-12); OLR Research Report 2025-R-0152 (checked 2026-10-12); 2025 R 0152 (checked 2026-09-27); 2025 Form CT-1040 instructions (archived copy): Schedule 1 line 48b (checked 2026-10-12); Publication 525 (checked 2026-10-12) - Disability pay outside the pension subtraction only when the caller gives the person facts (a civil service annuity, disability pay, Social Security disability, survivor benefits, an IRA basis or an exception) Where disability pay received before the employer's minimum retirement age is wages, the pay leaves the pool the pension subtraction draws on and re-enters the base in full after the exclusions, unless planMinimumRetirementAge says the person has reached that age. Per person by the caller's split, else equally. A person at or past the plan's minimum retirement age (when given) receives a disability pension, which stays in the pool.
Connecticut's values · engine step (compute_state_tax_detail). Sources (IRA, 401(k) and private pensions): 2025 Form CT-1040 Instructions (checked 2026-10-12); OLR Research Report 2025-R-0152 (checked 2026-10-12); 2025 R 0152 (checked 2026-09-27); 2025 Form CT-1040 instructions (archived copy): Schedule 1 line 48b (checked 2026-10-12); Publication 525 (checked 2026-10-12) - Keeping the per-spouse shares inside the household joint returns with each spouse's own amounts given After the public-pension and employer-pension carve-outs, if the two spouses' remaining shares add up to more than the household's exclusion-eligible distributions (an inconsistent split), spouse 1's share is reduced so they do not.
engine step (compute_state_tax_detail). Engine convention, no external source: Input normalisation. - Military retirement pay The state's military rule runs first, on military pay alone, per taxpayer: each spouse's own pay at their own age when attributed, otherwise half each at the household age on a joint return. Exempt dollars leave the base; the rest become pension dollars for the general retirement rules. Where the state lets a disabled retiree qualify at any age, a disabled person is treated as having reached the rule's age.
Connecticut's values · engine step (compute_state_tax_detail). Sources (Military retirement pay): Chap 229 (checked 2026-09-27) - One taxpayer's military exemption Exempt: all of it (below the age split, up to the younger cap). Capped: up to the cap for the age tier, plus the earned-income bonus below the age split when the taxpayer's own wages exceed the threshold, less the taxpayer's own Social Security where the rule says so. Percentage: the percentage (below the age split, up to the younger cap). Then the income limit: above it the exemption is lost, or phased out over the range where one is set.
Connecticut's values · engine step (military_exempt_one). Sources (Military retirement pay): Chap 229 (checked 2026-09-27) - Capital-loss deduction off the base The deduction comes off the other ordinary income (negative income, as Form 1040 line 7a is), so the base and every state-AGI figure summed from it carry it; WI no more than Wisconsin ordinary income (Schedule WD line 28(c)). States whose base is federal taxable income (with the caller's figure) already have it there and take it only once. Engine 1.13.1: the allowed rental loss comes off the same way, on its own line (rental_loss_deduction).
Connecticut's values · engine step (compute_state_tax_detail). Sources (Capital gains): 2025 Form CT-1040 Instructions (checked 2026-10-12); 2025 Form CT-1040 TCS, Tax Calculation Schedule (checked 2026-09-28); 2025 Schedule D (Form 1040), Capital Gains and Losses (checked 2026-10-12) - Which Social Security threshold applies Joint returns use the joint threshold; head of household uses it too where the state says so, otherwise the single one; married filing separately uses its own threshold where set, else the single one. Benefits are tested against the income total above.
Connecticut's values · engine step (ss_amount_in_state_base). Sources (Social Security): 2025 Form CT-1040 Instructions (checked 2026-10-12); OLR Research Report 2025-R-0152 (checked 2026-10-12); 2025 Form CT-1040 instructions (archived copy): Social Security Benefit Adjustment Worksheet (checked 2026-10-12) - Social Security: a share of gross benefits above a threshold At or below the threshold nothing enters. Above it, 12.75% of gross benefits, capped at the federally taxable amount; without gross benefits the engine estimates them as the taxable amount divided by 0.85.
Connecticut's values · engine step (ss_amount_in_state_base). Sources (Social Security): 2025 Form CT-1040 Instructions (checked 2026-10-12); OLR Research Report 2025-R-0152 (checked 2026-10-12); 2025 Form CT-1040 instructions (archived copy): Social Security Benefit Adjustment Worksheet (checked 2026-10-12) - Income-tested percentage of distributions Distributions are deductible at the percentage for the income band (joint column for joint returns, and for head of household unless it uses the single column). Where the state says so a conversion draws the same percentage; otherwise it is taxed in full. In per-person mode the excluded amount is shown for each spouse in proportion to their own distributions (reporting only).
Connecticut's values · engine step (compute_state_tax_detail). Sources (IRA, 401(k) and private pensions): 2025 Form CT-1040 Instructions (checked 2026-10-12); OLR Research Report 2025-R-0152 (checked 2026-10-12); 2025 R 0152 (checked 2026-09-27); 2025 Form CT-1040 instructions (archived copy): Schedule 1 line 48b (checked 2026-10-12); Publication 525 (checked 2026-10-12) - The percentage table The deductible share by income. Single, head-of-household and separate filers: 100% from $0; 85% from $75,000; 70% from $77,500; 55% from $80,000; 40% from $82,500; 25% from $85,000; 10% from $87,500; 5% from $90,000; 2.5% from $95,000; 0% from $100,000. Joint filers: 100% from $0; 85% from $100,000; 70% from $105,000; 55% from $110,000; 40% from $115,000; 25% from $120,000; 10% from $125,000; 5% from $130,000; 2.5% from $140,000; 0% from $150,000. The table lives in code; these values are read back from it.
Connecticut's values · engine step (ct_pension_deductible_pct). Sources (IRA, 401(k) and private pensions): 2025 Form CT-1040 Instructions (checked 2026-10-12); OLR Research Report 2025-R-0152 (checked 2026-10-12); 2025 R 0152 (checked 2026-09-27); 2025 Form CT-1040 instructions (archived copy): Schedule 1 line 48b (checked 2026-10-12); Publication 525 (checked 2026-10-12) - Long-term gains in the base Where gains are taxed as ordinary income: net long-term gain less the flat exclusion (never below zero), times the inclusion share. Elsewhere none enters.
Connecticut's values · engine step (compute_state_tax_detail). Sources (Capital gains): 2025 Form CT-1040 Instructions (checked 2026-10-12); 2025 Form CT-1040 TCS, Tax Calculation Schedule (checked 2026-09-28); 2025 Schedule D (Form 1040), Capital Gains and Losses (checked 2026-10-12) - Exemption phase-out on state income The exemption the engine carries as the deduction is lost in whole steps for each step (or part) of income over the start, or linearly over the range; the income here is what enters the state base (exempt Social Security left out).
Connecticut's values · engine step (compute_state_tax_detail). Sources (Deductions, exemptions and credits): 2025 Form CT-1040 TCS, Tax Calculation Schedule (checked 2026-09-28); Chap 229 (checked 2026-09-28); 2025 Form CT-1040 Instructions (checked 2026-10-12); 2026 Supplement to the General Statutes, chapter 229 (checked 2026-10-01); 2025 Form CT-1040 Instructions, Schedule 3 Property Tax Credit (checked 2026-10-01) - State taxable income Other ordinary income + Social Security, retirement income, conversion and gains left in the base − standard deduction − personal exemption − age subtractions.
engine step (compute_state_tax_detail). Engine convention, no external source: The order of subtraction follows the state forms; each amount is sourced at its own step. - No tax at or below zero State taxable income at or below zero returns a tax of 0 (credits are not refundable), unless the state has a tax computed apart from taxable income that still applies (next step).
engine step (compute_state_tax_detail). Engine convention, no external source: Every credit the engine carries is nonrefundable, so nothing below can make a zero tax negative; each credit is sourced at its own step. - Separate-return scaling married filing separately For the halved-joint rule, taxable income is doubled before the schedule and the result halved.
Connecticut's values · engine step (compute_state_tax_detail). Sources (Rate schedule): 2025 Form CT-1040 TCS, Tax Calculation Schedule (checked 2026-09-27) - The rate schedule Each bracket's rate on the part of taxable income inside it, summed. No rounding: the result is carried in full precision.
Connecticut's values · engine step (apply_state_brackets). Sources (Rate schedule): 2025 Form CT-1040 TCS, Tax Calculation Schedule (checked 2026-09-27) - Add-back and recapture On state AGI (the income in the base), the add-back and the recapture below are added to the schedule tax.
Connecticut's values · engine step (compute_state_tax_detail). Sources (Surtaxes and recapture): 2025 Form CT-1040 TCS, Tax Calculation Schedule (checked 2026-09-27) - Rate phase-out add-back (Table C) A fixed amount per step (or part) of income over the start, up to a maximum, by filing status. The table lives in code; the state page prints engine values.
Connecticut's values · engine step (ct_2pct_phaseout_addback). Sources (Surtaxes and recapture): 2025 Form CT-1040 TCS, Tax Calculation Schedule (checked 2026-09-27) - Personal tax credit table (Table E) The decimal of the first row whose income limit holds the state AGI, by filing status (.75 down to .01; none above the last row). The table lives in code (statutory, unindexed; the TY2025 table is the 2026 proxy).
Connecticut's values · engine step (ct_personal_credit_decimal). Sources (Deductions, exemptions and credits): 2025 Form CT-1040 TCS, Tax Calculation Schedule (checked 2026-09-28); Chap 229 (checked 2026-09-28); 2025 Form CT-1040 Instructions (checked 2026-10-12); 2026 Supplement to the General Statutes, chapter 229 (checked 2026-10-01); 2025 Form CT-1040 Instructions, Schedule 3 Property Tax Credit (checked 2026-10-01) - Benefit recapture (Table D) Three tiers per filing status (separate returns use the single tiers); each adds a fixed amount per step (or part) of income over its start, up to its own maximum.
Connecticut's values · engine step (ct_benefit_recapture). Sources (Surtaxes and recapture): 2025 Form CT-1040 TCS, Tax Calculation Schedule (checked 2026-09-27) - Personal tax credit (a decimal of the tax) A credit of the Table E decimal times the tax before credits (the schedule with the add-back and recapture), by state AGI and filing status; carried with the personal credits.
Connecticut's values · engine step (compute_state_tax_detail). Sources (Deductions, exemptions and credits): 2025 Form CT-1040 TCS, Tax Calculation Schedule (checked 2026-09-28); Chap 229 (checked 2026-09-28); 2025 Form CT-1040 Instructions (checked 2026-10-12); 2026 Supplement to the General Statutes, chapter 229 (checked 2026-10-01); 2025 Form CT-1040 Instructions, Schedule 3 Property Tax Credit (checked 2026-10-01) - Credits cannot make the tax negative The credits are subtracted and the result floored at zero.
engine step (compute_state_tax_detail). Engine convention, no external source: Every credit the engine carries is nonrefundable; each credit is sourced at its own step. - Qualifying surviving spouse qualifying surviving spouse returns A qualifying surviving spouse (
filingStatusqss) is one person on the return, taxed from the single figures with the state's own treatment of the status laid over them: where the state says so, the joint rate schedule, the joint standard deduction, the joint personal exemption, the joint income limits and phase-outs (only those the state sets for joint returns), the married 65+ and blindness amounts, or the head-of-household return; where the state gives the status nothing of its own, the single return. The federal figures the engine derives for the status are the federal qualifying-surviving-spouse ones (the joint standard deduction, the married 65+ amount).
Connecticut's values · engine step (state_tax_effective_config). Sources (Rate schedule): 2025 Form CT-1040 TCS, Tax Calculation Schedule (checked 2026-09-27) - Railroad Retirement benefits only when the caller gives Railroad Retirement benefits Railroad Retirement benefits are never taxed by a state (45 U.S.C. §231m). Tier 2 (
railroadRetirementTier2) is in the income total the tests use but never in the base. Tier 1 (railroadRetirementTier1) is a part of the gross benefits (socialSecurityGross); its share of the taxable benefits is taken out of the Social Security every state rule sees, so a state that taxes Social Security never reaches it. Where a state's worksheet says so, the benefits reduce a retirement cap or subtraction (ID, IN, MD, ME, MN: both tiers; MI: the taxable railroad benefits); Minnesota's and Utah's Social Security rules test an income without them, Minnesota's, New Jersey's and California's retirement income tests an income without Tier 2; Ohio and Delaware test their own AGI everywhere, which never holds the benefits.
Connecticut's values · engine step (compute_state_tax_detail). Sources (Social Security): 2025 Form CT-1040 Instructions (checked 2026-10-12); OLR Research Report 2025-R-0152 (checked 2026-10-12); 2025 Form CT-1040 instructions (archived copy): Social Security Benefit Adjustment Worksheet (checked 2026-10-12) - The capital-loss deduction the state allows With a net capital loss (capitalLoss): the smaller of the loss and the state's limit (the federal $3,000 / $1,500 where the state follows the federal return; MA $2,000, and no more than the interest and dividends); AL the loss less the part carried in, unlimited; PA and NJ none. It comes off the income total the income tests use (and the Social Security worksheets' income); the gross-income filing test (LA) reads the total before it. Engine 1.13.1: with a rental loss (rentalNetIncome below 0, the federal Schedule E line 26 amount) the state allows, the whole loss where the state starts from federal AGI or follows the federal schedule, none in PA and NJ (rental_loss_no_offset): it comes off the same income the same way; a rental profit is other ordinary income.
Connecticut's values · engine step (compute_state_tax_detail). Sources (Capital gains): 2025 Form CT-1040 Instructions (checked 2026-10-12); 2025 Form CT-1040 TCS, Tax Calculation Schedule (checked 2026-09-28); 2025 Schedule D (Form 1040), Capital Gains and Losses (checked 2026-10-12) - Each spouse's own Social Security joint returns On a joint return, each spouse's own Social Security is the spouse's share of the benefits by
spouse.socialSecurityGrosswhen the caller gives it (Tier 1 railroad benefits left out), else half each. It is what the per-spouse rules read: Colorado's per-spouse subtraction, Rhode Island's per-spouse modification, and the Maine, Maryland and other retirement caps reduced by the benefits each spouse received (with each spouse's own railroad benefits where the state counts them).
Connecticut's values · engine step (compute_state_tax_detail). Sources (Social Security): 2025 Form CT-1040 Instructions (checked 2026-10-12); OLR Research Report 2025-R-0152 (checked 2026-10-12); 2025 Form CT-1040 instructions (archived copy): Social Security Benefit Adjustment Worksheet (checked 2026-10-12) - Refundable state credits The credits paid beyond the tax (reported in refundableCredits; netTax = totalTax less them): earned income credits as a share of the federal EIC with each state's own age band (OK on the 2020 federal credit, DC's own childless schedule, the CalEITC table, MN's Working Family Credit), the NYC EIC and school tax credits, and the property-tax, renter, grocery and senior credits of MA, MI, NJ, ID, HI, NM, OK, AZ, NY, RI, WV, ME, DC, MN, MO, WI, IN and MT, each on its own income measure. Engine 1.13.1: a part-year NYC resident's school tax credits (the Table 2 proration chart and the rate-reduction amount on IT-360.1 line 47; IT-203 lines 60 / 60a for a part-year state resident).
Connecticut's values · engine step (state_tax_refundable_credits). Sources (Deductions, exemptions and credits): 2025 Form CT-1040 TCS, Tax Calculation Schedule (checked 2026-09-28); Chap 229 (checked 2026-09-28); 2025 Form CT-1040 Instructions (checked 2026-10-12); 2026 Supplement to the General Statutes, chapter 229 (checked 2026-10-01); 2025 Form CT-1040 Instructions, Schedule 3 Property Tax Credit (checked 2026-10-01) - Property tax credit (CT) Schedule 3: the property tax, at most $300, less a share for each AGI step over the start, nonrefundable.
Connecticut's values · engine step (st_compute). Sources (Deductions, exemptions and credits): 2025 Form CT-1040 TCS, Tax Calculation Schedule (checked 2026-09-28); Chap 229 (checked 2026-09-28); 2025 Form CT-1040 Instructions (checked 2026-10-12); 2026 Supplement to the General Statutes, chapter 229 (checked 2026-10-01); 2025 Form CT-1040 Instructions, Schedule 3 Property Tax Credit (checked 2026-10-01)
Rate schedule
Single
| Taxable income from | to | Rate |
|---|---|---|
| $0 | $10,000 | 2% |
| $10,000 | $50,000 | 4.5% |
| $50,000 | $100,000 | 5.5% |
| $100,000 | $200,000 | 6% |
| $200,000 | $250,000 | 6.5% |
| $250,000 | $500,000 | 6.9% |
| $500,000 | and up | 6.99% |
Married filing jointly
| Taxable income from | to | Rate |
|---|---|---|
| $0 | $20,000 | 2% |
| $20,000 | $100,000 | 4.5% |
| $100,000 | $200,000 | 5.5% |
| $200,000 | $400,000 | 6% |
| $400,000 | $500,000 | 6.5% |
| $500,000 | $1,000,000 | 6.9% |
| $1,000,000 | and up | 6.99% |
Head of household
| Taxable income from | to | Rate |
|---|---|---|
| $0 | $16,000 | 2% |
| $16,000 | $80,000 | 4.5% |
| $80,000 | $160,000 | 5.5% |
| $160,000 | $320,000 | 6% |
| $320,000 | $400,000 | 6.5% |
| $400,000 | $800,000 | 6.9% |
| $800,000 | and up | 6.99% |
Married filing separately: the engine computes the MFJ tax on twice the income and halves it, which is the same as halving every MFJ threshold and the MFJ deduction.
Source review notes (what the sources do not state outright, or what the engine does not carry):
- No 2026 TCS was available; the TY2025 (Rev. 12/25) schedule is the proxy.
- CGS 12-700(a) statute text unreachable (cga.ct.gov timeout).
- 2025 Form CT-1040 TCS, Tax Calculation Schedule, Connecticut Department of Revenue Services (archived copy). Connecticut's 2025 Table B applies 2%, 4.5%, 5.5%, 6%, 6.5%, 6.9% and 6.99% with single edges at $10k/$50k/$100k/$200k/$250k/$500k, MFJ edges doubled, and HOH edges at 1.6x single. Checked 2026-09-27.
Deductions, exemptions and credits
- Standard deduction (or the exemption the engine carries in its place): $15,000 single, $24,000 married filing jointly, $19,000 head of household.
- The exemption is lost $1,000 for each $1,000 (or part) of income above $30,000 (single), $38,000 (head of household), $24,000 (married filing separately) and $48,000 (MFJ), until it is gone.
Source review notes (what the sources do not state outright, or what the engine does not carry):
- CGS 12-702 and OLR 2024-R-0130 (cited in code) unreachable.
- 2025 Form CT-1040 TCS, Tax Calculation Schedule, Connecticut Department of Revenue Services (archived copy). Connecticut's personal exemption is $15,000 single / $24,000 MFJ / $19,000 HOH and is reduced $1,000 per $1,000 of CT AGI above $30,000 / $48,000 / $38,000 (Table A). Checked 2026-09-28.
- Chap 229, Connecticut General Assembly (archived copy). Connecticut General Assembly: "the exemption amount shall be reduced by one thousand dollars for each one thousand dollars, or fraction thereof" Earned income credit (engine 1.12.0, refundableCredits): 40% of the federal EIC plus $250 with a qualifying child. Property tax credit (engine 1.12.0): Schedule 3, the property tax paid up to $300, less 15% per $10,000 of CT AGI over the start, nonrefundable. Checked 2026-09-28.
- Form CT-1040 TCS (Rev. 12/25), Table E Personal Tax Credits (archived copy), Connecticut Department of Revenue Services. Engine 1.8.0: TCS lines 8-10 — a credit of a decimal (.75 down to .01) of the line 7 tax by CT AGI and filing status, none from $64,500 single / $100,500 joint / $52,500 separate / $78,500 head of household (table in code). Checked 2026-09-28.
- 2025 Form CT-1040 Instructions, Connecticut Department of Revenue Services. Earned income credit (engine 1.12.0, refundableCredits): 40% of the federal EIC plus $250 with a qualifying child. Property tax credit (engine 1.12.0): Schedule 3, the property tax paid up to $300, less 15% per $10,000 of CT AGI over the start, nonrefundable. Checked 2026-10-12.
- 2026 Supplement to the General Statutes, chapter 229, Connecticut General Assembly. Property tax credit (engine 1.12.0): Schedule 3, the property tax paid up to $300, less 15% per $10,000 of CT AGI over the start, nonrefundable. Checked 2026-10-01.
- 2025 Form CT-1040 Instructions, Schedule 3 Property Tax Credit, Connecticut Department of Revenue Services. Property tax credit (engine 1.12.0): Schedule 3, the property tax paid up to $300, less 15% per $10,000 of CT AGI over the start, nonrefundable. Checked 2026-10-01.
IRA, 401(k) and private pensions
- Pension, annuity and IRA distributions are deductible at a percentage set by income. Single, head of household and married filing separately: 100% from $0; 85% from $75,000; 70% from $77,500; 55% from $80,000; 40% from $82,500; 25% from $85,000; 10% from $87,500; 5% from $90,000; 2.5% from $95,000; 0% from $100,000. Married filing jointly: 100% from $0; 85% from $100,000; 70% from $105,000; 55% from $110,000; 40% from $115,000; 25% from $120,000; 10% from $125,000; 5% from $130,000; 2.5% from $140,000; 0% from $150,000. Head of household uses the single column.
- 2025 Form CT-1040 Instructions, Connecticut Department of Revenue Services (archived copy). Pension/annuity and traditional-IRA distributions are subtracted at a percentage stepping from 100% below $75,000 federal AGI (single/MFS/HOH) or $100,000 (MFJ) down to 0% at $100,000 / $150,000; for 2025 only 75% of IRA distributions entered the worksheet. Checked 2026-10-12.
- OLR Research Report 2025-R-0152, Connecticut General Assembly, Office of Legislative Research (archived copy). OLR confirms the IRA deduction uses the same phase-out table and is 100% beginning in 2026 (75% in 2025), and that head-of-household filers use the single/MFS thresholds. Checked 2026-10-12.
- 2025 R 0152, Connecticut General Assembly (archived copy). Connecticut General Assembly: "The deduction is 75% for 2025 and 100% beginning in 2026." Checked 2026-09-27.
- 2025 Form CT-1040 instructions (archived copy): Schedule 1 line 48b, Connecticut Department of Revenue Services. Engine 1.8.0: disability pay received before the employer's minimum retirement age is not a pension for line 48b; without planMinimumRetirementAge (engine 1.8.0 final) the engine reads disability pay as received before that age and subtracts none; with it, the pay is a pension for line 48b from that age. Checked 2026-10-12.
- Publication 525, Internal Revenue Service. Disability pay is wages until the plan's minimum retirement age and a pension from the day after it: with planMinimumRetirementAge given, CT line 48b subtracts it from that age (engine 1.8.0 final). Checked 2026-10-12.
Public pensions
No separate treatment: public pensions follow the rules for other retirement income above.
Source review notes (what the sources do not state outright, or what the engine does not carry):
- The 50% Connecticut teachers' retirement alternative is not modeled; the engine applies the general phase-down to other pensions.
- 2025 Form CT-1040 Instructions, Connecticut Department of Revenue Services (archived copy). Government pensions get the same phase-down subtraction as private pensions; Connecticut Teachers' Retirement System pay may instead take a 50% subtraction (no double benefit); military retirement pay is fully exempt. Checked 2026-10-12.
- OLR Research Report 2025-R-0152, Connecticut General Assembly, Office of Legislative Research (archived copy). OLR: TRS pensioners may deduct 50% of TRS income or use the general pension exemption, whichever is more favorable. Checked 2026-09-27.
Military retirement pay
- Military retirement pay is fully exempt, at any age.
- Rules are applied per taxpayer at that person's own age when the spouse's age is given. API value:
rules.militaryRetirement.treatment: "exempt".
- Chap 229, Connecticut General Assembly (archived copy). Military retirement pay from the United States is exempt from Connecticut income tax, separately from the general pension subtraction. Checked 2026-09-27.
Roth conversions
A conversion is part of the IRA line the income-tested percentage applies to, so it draws the same deductible percentage as other IRA distributions.
- 2025 Form CT-1040 Instructions, Connecticut Department of Revenue Services (archived copy). Connecticut starts from federal AGI (Form 1040 line 11a), so a Roth conversion enters CT AGI. A taxable conversion is part of the IRA amount on federal Form 1040 line 4b, which the Schedule 1 pension and IRA subtraction starts from, so the engine gives it the same deductible percentage (by CT AGI band) as other IRA distributions (engine 1.2.0). Checked 2026-10-12.
- 2025 R 0152, Connecticut General Assembly (archived copy). Connecticut General Assembly: "The deduction is 75% for 2025 and 100% beginning in 2026." Checked 2026-09-27.
Capital gains
- Net long-term gain is taxed as ordinary income.
- Short-term gains are ordinary income.
- 2025 Form CT-1040 Instructions, Connecticut Department of Revenue Services (archived copy). Capital gains enter CT AGI through federal AGI and are taxed under the same Table B rates as other income. Checked 2026-10-12.
- 2025 Form CT-1040 TCS, Tax Calculation Schedule, Connecticut Department of Revenue Services (archived copy). One rate table (Table B) applies to all Connecticut taxable income; there is no separate capital-gains rate. Checked 2026-09-28.
- 2025 Schedule D (Form 1040), Capital Gains and Losses, Internal Revenue Service. The federal return deducts a net capital loss up to $3,000 ($1,500 married filing separately) on Form 1040 line 7a; a state that starts from federal adjusted gross income or federal taxable income carries that deduction. Checked 2026-10-12.
Surtaxes and recapture
- The 2% rate phase-out add-back and the benefit recapture are added to the bracket tax. Engine values at sample incomes (add-back + recapture):
Income Single MFJ HOH MFS $50,000 $0 + $0 $0 + $0 $0 + $0 $0 + $0 $60,000 $25 + $0 $0 + $0 $0 + $0 $100 + $0 $100,000 $225 + $0 $0 + $0 $240 + $0 $250 + $0 $150,000 $250 + $225 $500 + $0 $400 + $0 $250 + $225 $250,000 $250 + $1,150 $500 + $200 $400 + $400 $250 + $1,150 $500,000 $250 + $2,950 $500 + $2,300 $400 + $3,620 $250 + $2,950 $1,100,000 $250 + $3,400 $500 + $6,800 $400 + $5,320 $250 + $3,400
Source review notes (what the sources do not state outright, or what the engine does not carry):
- CGS 12-700(a) (cited in code) unreachable.
- 2025 Form CT-1040 TCS, Tax Calculation Schedule, Connecticut Department of Revenue Services (archived copy). Above set CT AGI levels, Table C adds back the 2% bracket benefit (max $250 single / $500 MFJ / $250 MFS / $400 HOH) and Table D recaptures lower-bracket benefits in three tiers (max $3,400 single / $6,800 MFJ / $5,320 HOH). Checked 2026-09-27.
Part-year and nonresident returns
- Part-year resident (CT-1040NR/PY): the tax a full-year resident would owe on all the year's income, times the state's income ratio.
- Nonresident (CT-1040NR/PY): the tax a full-year resident would owe on all the year's income, times the state's income ratio.
- The ratio: the state's own AGI (after its subtractions) of the state's income over the state AGI of the whole year, rounded to 4 places, at most 1.
- The tax on the greater of Connecticut AGI and Connecticut-source income, × the ratio; no tax when both are zero or less.
- A nonresident's retirement income is not taxable by the state (4 U.S.C. §114); the API refuses it in
residency.stateIncome. The credit for tax paid to another state and the earned income credits on these returns are not computed.
Married couples whose residency differs (engine 1.13.0)
With residency.spouse on a joint request, each allowed treatment is calculated and reported in residency.couple; tax is the required one, else the state's default, else the couple's residency.election, else the joint return the request's mfj names. Each rule is quoted from the state's instructions (engine 1.14.0: and its statutes, regulations, bulletins and other official guidance) in the sources below.
| Spouses | Connecticut's rule |
|---|---|
| One spouse a full-year resident, the other a part-year resident | separate returns is required. |
| One spouse a full-year resident, the other a nonresident | separate returns, unless the couple elects a joint resident return (both taxed as full-year residents). |
| One spouse a part-year resident, the other a nonresident | separate returns is required. |
| Both part-year residents, different resident periods | separate returns is required. |
| Both nonresidents, only one with income from the state | separate returns, unless the couple elects a joint part-year / nonresident return. |
- 2025 Form CT-1040NR/PY Instructions (Rev. 12/25) (Wayback copy), Connecticut Department of Revenue Services. Part-year / nonresident return (engine 1.12.0, residency): Tax computed (resident method, incl. personal credit/phase-outs) on the GREATER of CT AGI (line 5) or CT-source income (line 6), then multiplied by line 9 = line 6 / line 5 (if line 5 > line 6; otherwise 1.0000). Checked 2026-10-01.
- Form CT-1040 Connecticut Resident Income Tax Return Instructions (2025, Rev. 12/25), Connecticut Department of Revenue Services. Married couples whose residency differs (engine 1.13.0): Checked 2026-10-06.
Worked examples
Computed by the engine for the fixed households below (the same ones for every state, so states compare directly). Federal tax is not supplied, so a federal-tax deduction is not taken; the income tests use the sum of the components as income.
| Household (engine inputs) | State tax |
|---|---|
| Single, 67: $30,000 private pension, $20,000 IRA, $10,000 interest, $24,000 Social Security ($17,000 federally taxable), $5,000 long-term gain | $1,496.25 |
| Married filing jointly, 70: $40,000 public pension, $40,000 IRA, $20,000 interest, $40,000 Social Security ($34,000 federally taxable), $10,000 long-term gain | $5,190 |
| Single, 60: $60,000 other ordinary income and a $50,000 Roth conversion | $5,625 |
| Married filing jointly, 66: $30,000 IRA, a $40,000 Roth conversion, $30,000 Social Security ($25,500 federally taxable) | $0 |
| Single, 58: $36,000 military retirement pay and $30,000 wages | $361.25 |
| Married filing jointly, ages 67 and 61: $50,000 IRA, $10,000 interest, $30,000 Social Security ($25,500 federally taxable), each spouse's age given | $0 |
Line by line
The intermediate lines the engine records while it computes each example (its detail record, printed as it comes out; lines that are zero are left out). The engine's documentation build checks that the lines add up to the taxable income and the tax, for every state, filing status and a grid of households. Each line links the engine step that produces it.
Single, 67: $30,000 private pension, $20,000 IRA, $10,000 interest, $24,000 Social Security ($17,000 federally taxable), $5,000 long-term gain: $1,496.25
| Line | Amount |
|---|---|
| Income total used by the income tests | $82,000 |
| Retirement income and conversions excluded (not in the base) | $27,500 |
| + Other ordinary income in the base | $10,000 |
| + Social Security in the base | $6,000 |
| + Retirement income in the base | $22,500 |
| + Long-term gain in the base | $5,000 |
| − Standard deduction | $1,000 |
| = State taxable income | $42,500 |
| Tax from the rate schedule | $1,662.50 |
| = Tax before credits | $1,662.50 |
| Per-exemption credit | $166.25 |
| − Credits used (never more than the tax) | $166.25 |
| = Tax | $1,496.25 |
Married filing jointly, 70: $40,000 public pension, $40,000 IRA, $20,000 interest, $40,000 Social Security ($34,000 federally taxable), $10,000 long-term gain: $5,190
| Line | Amount |
|---|---|
| Income total used by the income tests | $144,000 |
| Retirement income and conversions excluded (not in the base) | $2,000 |
| + Other ordinary income in the base | $20,000 |
| + Social Security in the base | $10,000 |
| + Retirement income in the base | $78,000 |
| + Long-term gain in the base | $10,000 |
| = State taxable income | $118,000 |
| Tax from the rate schedule | $4,990 |
| + Rate phase-out add-back (Table C) | $200 |
| = Tax before credits | $5,190 |
| = Tax | $5,190 |
Single, 60: $60,000 other ordinary income and a $50,000 Roth conversion: $5,625
| Line | Amount |
|---|---|
| Income total used by the income tests | $110,000 |
| + Other ordinary income in the base | $60,000 |
| + Roth conversion in the base | $50,000 |
| = State taxable income | $110,000 |
| Tax from the rate schedule | $5,350 |
| + Rate phase-out add-back (Table C) | $250 |
| + Benefit recapture (Table D) | $25 |
| = Tax before credits | $5,625 |
| = Tax | $5,625 |
Married filing jointly, 66: $30,000 IRA, a $40,000 Roth conversion, $30,000 Social Security ($25,500 federally taxable): $0
| Line | Amount |
|---|---|
| Income total used by the income tests | $95,500 |
| Retirement income and conversions excluded (not in the base) | $70,000 |
| − Standard deduction | $24,000 |
| = State taxable income | $0 |
| Tax from the rate schedule | $0 |
| = Tax | $0 |
Single, 58: $36,000 military retirement pay and $30,000 wages: $361.25
| Line | Amount |
|---|---|
| Income total used by the income tests | $66,000 |
| Military pay excluded (not in the base) | $36,000 |
| + Other ordinary income in the base | $30,000 |
| − Standard deduction | $15,000 |
| = State taxable income | $15,000 |
| Tax from the rate schedule | $425 |
| = Tax before credits | $425 |
| Per-exemption credit | $63.75 |
| − Credits used (never more than the tax) | $63.75 |
| = Tax | $361.25 |
Married filing jointly, ages 67 and 61: $50,000 IRA, $10,000 interest, $30,000 Social Security ($25,500 federally taxable), each spouse's age given: $0
After 2026: how the amounts move
A request with projection (API) estimates a later tax year from these rules: every
dollar amount and age test below moves the way Connecticut's law moves it. Rates and the rules themselves stay the 2026 ones
(how projection works).
| Amounts (engine fields) | After 2026 | What the law says, and the source |
|---|---|---|
brackets_single (the single rate schedule's thresholds), brackets_mfj (the mfj rate schedule's thresholds), brackets_hoh (the hoh rate schedule's thresholds), ct-table-c-addback (a table held in code), ct-table-d-recapture (a table held in code) | Fixed in law: held at the rules-year amount in every later year. | CGS 12-700(a)(10) prints the rate schedules for taxable years on or after January 1, 2024 (2%/4.5%/5.5%/6%/6.5%/6.9%/6.99%) together with the phase-out of the lowest rate (Table C, from $56,500 single) and the benefit recapture (Table D, from $105,000 / $200,000 single) as fixed dollar amounts; chapter 229 contains no inflation adjustment.
|
std_deduction_single, std_deduction_mfj, std_deduction_hoh, exemption_phaseout_start_single, exemption_phaseout_start_mfj, exemption_phaseout_start_hoh, exemption_phaseout_start_mfs, exemption_phaseout_range_single, exemption_phaseout_range_mfj, exemption_phaseout_step | Fixed in law: held at the rules-year amount in every later year. | CGS 12-702: personal exemption $15,000 single (2016+), $19,000 HOH, $24,000 joint, $12,000 MFS, each reduced $1,000 per $1,000 (or fraction) of Connecticut AGI above $30,000 / $38,000 / $48,000 / $24,000; fixed amounts.
|
ct-table-e-personal-credit (a table held in code) | Fixed in law: held at the rules-year amount in every later year. | CGS 12-703 sets the personal tax credit schedule by Connecticut AGI bands (e.g. single from $18,800); fixed amounts.
|
ss_exempt_agi_single, ss_exempt_agi_mfj, ct-ss-line-b-base (a table held in code) | Fixed in law: held at the rules-year amount in every later year. | CGS 12-701(a)(20)(B)(x): full Social Security subtraction below federal AGI of $75,000 (single/MFS) or $100,000 (joint/HOH), otherwise capped at 25% of benefits via the federal IRC 86 base amounts ($25,000/$32,000, fixed in IRC 86); no indexing.
|
ct-pension-phasedown-table (a table held in code) | Fixed in law: held at the rules-year amount in every later year. | CGS 12-701(a)(20)(B)(xx)-(xxix): pension/annuity and (from 2026, 100%) IRA subtraction below $75,000/$100,000 single and $100,000/$150,000 joint AGI, with the fixed phase-down percentage table above; fixed dollar bands.
|
dis_plan_age_rule | Attained age: the same age in every year. | Disability pensions received before the employer's minimum retirement age are wages (not pension income): an attained-age test set by the plan.
|
cap_loss_limit, cap_loss_limit_mfs | Fixed in law: held at the rules-year amount in every later year. | The state follows the federal net capital loss limit of IRC 1211(b): $3,000 ($1,500 MFS), a fixed amount with no inflation adjustment.
|
ct_ptc_max, ct_ptc_step, ct_ptc_start_single, ct_ptc_start_mfj, ct_ptc_start_hoh, ct_ptc_start_mfs | Fixed in law: held at the rules-year amount in every later year. | Conn. Gen. Stat. 12-704c sets the $300 maximum and the AGI thresholds and steps as dollar amounts with no adjustment clause: fixed in law.
|
Enacted for later years, not applied by the projection
None found: the research found no change enacted for years after 2026 beyond the schedules above.
What the engine does not calculate, and known approximations
- The Table E personal tax credit is computed (engine 1.8.0; the TY2025 table, statutory and unindexed, used for 2026).
- The add-back and recapture tables are the 2025 schedule (statutory, not indexed), used for 2026.
- Disability pay (disabilityIncome) draws the pension and annuity subtraction (Schedule 1 line 48b) only from the employer's minimum retirement age given in planMinimumRetirementAge (engine 1.8.0): without it the pay is read as received before that age (wages), so a disability pension received after it is overtaxed.
- The Social Security worksheet's Line B needs the gross benefits (socialSecurityGross); without them, and on a separate return (where Line B depends on whether the spouses lived together), the 25% rule is applied to Line A, which can only overstate the tax.
- The 50% Connecticut teachers' retirement alternative is not modeled; the engine applies the general phase-down to other pensions. (Public pensions)
- Subtractions for interest on United States obligations (and mutual-fund dividends from them), taxable state and local tax refunds, Connecticut Higher Education Trust and ABLE contributions are not calculated: the inputs do not separate these amounts. Sources: 2025 Form CT-1040 TCS, Tax Calculation Schedule (checked 2026-09-28); Chap 229 (checked 2026-09-28); 2025 Form CT-1040 Instructions (checked 2026-10-12); 2026 Supplement to the General Statutes, chapter 229 (checked 2026-10-01); 2025 Form CT-1040 Instructions, Schedule 3 Property Tax Credit (checked 2026-10-01).
- The pension and annuity subtraction for disability pay received after the employer's minimum retirement age (a disability pension) is calculated only when planMinimumRetirementAge gives that age (engine 1.8.0): without it disabilityIncome cannot say whether the pay was received before that age, when it is wages, so disability pay is taxed in full. Sources: 2025 Form CT-1040 Instructions (checked 2026-10-12); OLR Research Report 2025-R-0152 (checked 2026-10-12); 2025 R 0152 (checked 2026-09-27); 2025 Form CT-1040 instructions (archived copy): Schedule 1 line 48b (checked 2026-10-12); Publication 525 (checked 2026-10-12).
- The Social Security worksheet's Line B is not applied on a separate return or without the gross benefits: on a separate return it depends on whether the spouses lived together, which the input does not say; the worksheet then uses the gross benefits (Line A), which can only overstate the tax. Sources: 2025 Form CT-1040 Instructions (checked 2026-10-12); OLR Research Report 2025-R-0152 (checked 2026-10-12); 2025 Form CT-1040 instructions (archived copy): Social Security Benefit Adjustment Worksheet (checked 2026-10-12).
- The motor vehicle property tax (Schedule 3 lines 61 and 62) is not a separate input: the property tax credit reads propertyTaxPaid as the property tax on the primary residence, so a filer who also paid motor vehicle tax may add it there (Connecticut's other rules do not read propertyTaxPaid). Sources: 2025 Form CT-1040 TCS, Tax Calculation Schedule (checked 2026-09-28); Chap 229 (checked 2026-09-28); 2025 Form CT-1040 Instructions (checked 2026-10-12); 2026 Supplement to the General Statutes, chapter 229 (checked 2026-10-01); 2025 Form CT-1040 Instructions, Schedule 3 Property Tax Credit (checked 2026-10-01).
What the engine does not calculate for any state (itemized deductions, credits beyond those listed, part-year residents, and more) is listed on the calculation order page.
Verification
Worksheet-tested Unit and golden tests follow the CT-1040 Tax Calculation Schedule (Tables C and D) and the Social Security benefit adjustment worksheet.
- Golden scenarios (hand-computed expected tax, asserted to within $1):
S14,H07,CT02,CTREC1. - State-specific unit tests:
test_ss_threshold_exempts_low_income,test_ct_caps_taxable_ss_at_25pct,test_ct_hoh_uses_mfj_ss_threshold,test_v3_folds_v2,test_ct_exemption_phaseout,test_ct_pension_phasedown,test_ct_hoh_schedule,test_ct_ss_quarter_of_exact_gross,test_ss_gross_noop_where_law_uses_taxable,test_d11_ct_addback_recapture,test_ct_disability_pay,test_ct_breakdown,test_ct,test_worked_ratios,test_engine_paths,test_ct_table_a_and_pension_column,test_ct_per_person_excluded_reported. - Structural tests covering every state: 8.
- State forms and worksheets followed in the test derivations: CT-1040 Tax Calculation Schedule, Tables A-E; CT-1040 Social Security benefit adjustment worksheet; Schedule 1 line 41 (Social Security Benefit Adjustment Worksheet Lines A-F) and line 48b.
Social Security
Exempt when income is below $75,000 (single) and $100,000 (married filing jointly and head of household). Above it, the amount included is 12.75% of gross benefits, capped at the federally taxable amount (when gross benefits are not supplied, the engine estimates them as taxable / 0.85).
API value:
socialSecurityRule: "capped_25_percent". The engine's input is the federally taxable amount; income tests use the sum of the income components as the adjusted-gross-income proxy.Source review notes (what the sources do not state outright, or what the engine does not carry):