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State tax docs / States / Idaho

Idaho state income tax: engine rules, 2026

How the QuantCalc engine computes Idaho 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 · Age 65+ subtractions and credits · Social Security · IRA, 401(k) and private pensions · Public pensions · Military retirement pay · Roth conversions · Capital gains · Blindness and disability · 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 ID).

How the tax is computed

Every step the engine takes for Idaho, 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 Idaho'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):

SingleMarried filing jointlyMarried filing separatelyHead of household
Rate schedule usedsingle schedulejoint schedulejoint schedule, thresholds halvedhead-of-household schedule
Top rate5.3% from $4,8115.3% from $9,6225.3% from $4,8115.3% from $9,622
Standard deduction, under 65$16,100$32,200$16,100$24,150
Standard deduction at 70 (joint: both 70)$18,150$35,500$17,750$26,200
Personal exemptionnonenonenonenone
Age subtractions at 70 (joint: both 70)$6,000$12,000none$6,000
  1. 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.
  2. 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.
  3. 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.
    Idaho's values · engine step (select_brackets). Sources (Rate schedule): Individual Income Tax Rate Schedule (checked 2026-09-27); Idaho Code 63-3024 (checked 2026-09-27); SECT63 3024 (checked 2026-09-28)
  4. 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).
    Idaho's values · engine step (select_brackets). Sources (Rate schedule): Individual Income Tax Rate Schedule (checked 2026-09-27); Idaho Code 63-3024 (checked 2026-09-27); SECT63 3024 (checked 2026-09-28)
  5. 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.
    Idaho's values · engine step (select_brackets). Sources (Rate schedule): Individual Income Tax Rate Schedule (checked 2026-09-27); Idaho Code 63-3024 (checked 2026-09-27); SECT63 3024 (checked 2026-09-28)
  6. 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.
  7. Attributing income to each spouse joint returns with each spouse's own amounts given With a caller's split (the API's spouse object), 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 gives spouse.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.
  8. 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.
  9. 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.
    Idaho's values · engine step (compute_state_tax_detail). Sources (Military retirement pay): Idaho Code 63-3022A (archived copy) (checked 2026-10-12); 2026 Form 1040ES-ME (checked 2026-10-12); EFO00088 09 29 2025 (checked 2026-09-27); Sect63 3022a (checked 2026-09-27); Form 39R Instructions (archived copy) (checked 2026-09-27); Idaho Code §63-3022A (archived copy) (checked 2026-10-12)
  10. Employed military retiree under the age Where the state lets a retiree under its military age qualify while employed with enough employment income to have to file a federal return, a retiree whose own wages (the household's on the household path) reach the federal filing threshold for the status is treated as having reached the age.
    Idaho's values · engine step (compute_state_tax_detail). Sources (Military retirement pay): Idaho Code 63-3022A (archived copy) (checked 2026-10-12); 2026 Form 1040ES-ME (checked 2026-10-12); EFO00088 09 29 2025 (checked 2026-09-27); Sect63 3022a (checked 2026-09-27); Form 39R Instructions (archived copy) (checked 2026-09-27); Idaho Code §63-3022A (archived copy) (checked 2026-10-12)
  11. 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.
    Idaho's values · engine step (military_exempt_one). Sources (Military retirement pay): Idaho Code 63-3022A (archived copy) (checked 2026-10-12); 2026 Form 1040ES-ME (checked 2026-10-12); EFO00088 09 29 2025 (checked 2026-09-27); Sect63 3022a (checked 2026-09-27); Form 39R Instructions (archived copy) (checked 2026-09-27); Idaho Code §63-3022A (archived copy) (checked 2026-10-12)
  12. One military cap per joint return joint returns On a joint return the cap is one amount for the couple, over the pay of the spouses who pass the age test, reduced by the household's Social Security where the rule says so, then the income test.
    Idaho's values · engine step (compute_state_tax_detail). Sources (Military retirement pay): Idaho Code 63-3022A (archived copy) (checked 2026-10-12); 2026 Form 1040ES-ME (checked 2026-10-12); EFO00088 09 29 2025 (checked 2026-09-27); Sect63 3022a (checked 2026-09-27); Form 39R Instructions (archived copy) (checked 2026-09-27); Idaho Code §63-3022A (archived copy) (checked 2026-10-12)
  13. No retirement deduction on a separate return married filing separately Where the statute gives married taxpayers the deduction only on a joint return, a married-filing-separately return excludes no military pay and no non-covered public pension.
    Idaho's values · engine step (compute_state_tax_detail). Sources (Military retirement pay): Idaho Code 63-3022A (archived copy) (checked 2026-10-12); 2026 Form 1040ES-ME (checked 2026-10-12); EFO00088 09 29 2025 (checked 2026-09-27); Sect63 3022a (checked 2026-09-27); Form 39R Instructions (archived copy) (checked 2026-09-27); Idaho Code §63-3022A (archived copy) (checked 2026-10-12)
  14. 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).
    Idaho's values · engine step (compute_state_tax_detail). Sources (Capital gains): 2025 Form 40 Instructions (archived) (checked 2026-09-28); 2025 Schedule D (Form 1040), Capital Gains and Losses (checked 2026-10-12)
  15. Social Security exempt None of the federally taxable benefit enters the base.
    Idaho's values · engine step (ss_amount_in_state_base). Sources (Social Security): unsourced: No official Idaho source could be fetched: tax.idaho.gov and legislature.idaho.gov (and every *.idaho.gov host tried) refuse connections from this host. No secondary source for Idaho's Social Security exemption was verified either.
  16. Retirement exclusion (household) The distributions eligible for the exclusion go through the exclusion below. Taxable public-pension dollars left by a cap are not eligible; below the IRA age only employer-plan dollars are.
    Idaho's values · engine step (compute_state_tax_detail). Sources (IRA, 401(k) and private pensions): unsourced: No official page states in terms that Idaho has no general retirement exclusion; Idaho Code 63-3022A (see Public pensions and Military retirement pay) lists the only retirement benefits Idaho deducts.
  17. Conversion taxed or exempt In full-exclusion states a conversion is exempt at the qualifying age (at any age where the state says so). Elsewhere, unless pooled above, it is ordinary income taxed in full.
    Idaho's values · engine step (compute_state_tax_detail). Sources (Roth conversions): unsourced: No official Idaho source could be fetched: tax.idaho.gov and legislature.idaho.gov (and every *.idaho.gov host tried) refuse connections from this host.
  18. Federal filing threshold The federal gross-income filing threshold for the status: the state's (federal) standard deduction plus the 65+ amount per person 65 or older; a fixed amount for married filing separately.
    engine step (federal_filing_threshold). Sources: Form 40 Instructions (archived copy) (checked 2026-09-27); Publication 501 (2025), Dependents, Standard Deduction, and Filing Information (checked 2026-10-12)
  19. 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.
    Idaho's values · engine step (compute_state_tax_detail). Sources (Capital gains): 2025 Form 40 Instructions (archived) (checked 2026-09-28); 2025 Schedule D (Form 1040), Capital Gains and Losses (checked 2026-10-12)
  20. Public pension not covered by Social Security only when the caller says the pension was not covered by Social Security Only when the caller says the public pension was not covered: the smaller of the public pension still in the base and the cap, reduced above the income start (by a percentage per step, or linearly over a range). Where it is an election instead of the Social Security exclusion, the engine keeps whichever excludes more.
    Idaho's values · engine step (compute_state_tax_detail). Sources (Public pensions): Idaho Code 63-3022A (archived copy) (checked 2026-10-12); 2026 Form 1040ES-ME (checked 2026-10-12); Idaho Code 63-3022A (archived copy) (checked 2026-10-12); EFO00088 09 29 2025 (checked 2026-09-27)
  21. Non-covered pension: age test and shared cap only when the caller says the pension was not covered by Social Security Where the state sets them: only a recipient at or above the age qualifies (each spouse's own public pension in per-person mode); the cap is reduced by the Social Security received (gross when supplied) and by the military pay the same deduction already excluded. A disabled recipient qualifies from the lower disability age where the state sets one.
    Idaho's values · engine step (compute_state_tax_detail). Sources (Public pensions): Idaho Code 63-3022A (archived copy) (checked 2026-10-12); 2026 Form 1040ES-ME (checked 2026-10-12); Idaho Code 63-3022A (archived copy) (checked 2026-10-12); EFO00088 09 29 2025 (checked 2026-09-27)
  22. Additional standard deduction at 65 The unmarried amount for a single or head-of-household filer 65 or older, the married amount for each spouse 65 or older, added to the standard deduction before any phase-out.
    Idaho's values · engine step (compute_state_tax_detail). Sources (Deductions, exemptions and credits): Individual income tax rate schedule (checked 2026-09-28); SECT63 3024 (checked 2026-09-28); 2025 Idaho Form 40 instructions (archived copy) (checked 2026-09-28); Rev. Proc. 2025-32 (2026 inflation adjustments) (checked 2026-10-12)
  23. Additional standard deduction for blindness only when the caller says a person is blind or disabled The unmarried amount for a blind single or head-of-household filer, the married amount for each blind spouse, added to the standard deduction before any phase-out. Age and blindness are separate boxes, so a person 65 or older and blind gets both.
    Idaho's values · engine step (compute_state_tax_detail). Sources (Blindness and disability): 2025 Form 40 instructions (archived copy) (checked 2026-09-28); Rev. Proc. 2025-32 (2026 inflation adjustments) (checked 2026-10-12); Idaho Code 63-3022A (archived copy) (checked 2026-10-12)
  24. Federal senior deduction taken against the state base For each taxpayer 65 or older: the amount, reduced by the rate times the income total above the status's start (joint start on a joint return); none for married filing separately. In the states whose base is federal taxable income it is taken only when the caller does not supply that figure (it is already in it).
    Idaho's values · engine step (compute_state_tax_detail). Sources (Age 65+ subtractions and credits): 2025 Idaho Form 40 instructions (archived copy) (checked 2026-09-27); Idaho Code 63-3004 (archived copy) (checked 2026-09-27); 2025 Schedule 1-A (Form 1040), Part V Enhanced Deduction for Seniors (checked 2026-10-12); Rev. Proc. 2025-32 (2026 inflation adjustments) (checked 2026-10-12)
  25. 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.
  26. Flat tax on every required return A flat amount on every return the state requires: the income total at least the federal filing threshold for the status (the standard deduction with its 65+ amounts; a fixed amount when married filing separately); none when the filer or spouse is blind where the state says so. It is owed even with no taxable income.
    engine step (compute_state_tax_detail). Sources: Form 40 Instructions (archived copy) (checked 2026-09-27); Publication 501 (2025), Dependents, Standard Deduction, and Filing Information (checked 2026-10-12)
  27. 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.
  28. Separate-return scaling married filing separately For the halved-joint rule, taxable income is doubled before the schedule and the result halved.
    Idaho's values · engine step (compute_state_tax_detail). Sources (Rate schedule): Individual Income Tax Rate Schedule (checked 2026-09-27); Idaho Code 63-3024 (checked 2026-09-27); SECT63 3024 (checked 2026-09-28)
  29. 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.
    Idaho's values · engine step (apply_state_brackets). Sources (Rate schedule): Individual Income Tax Rate Schedule (checked 2026-09-27); Idaho Code 63-3024 (checked 2026-09-27); SECT63 3024 (checked 2026-09-28)
  30. 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.
  31. Qualifying surviving spouse qualifying surviving spouse returns A qualifying surviving spouse (filingStatus qss) 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).
    Idaho's values · engine step (state_tax_effective_config). Sources (Rate schedule): Individual Income Tax Rate Schedule (checked 2026-09-27); Idaho Code 63-3024 (checked 2026-09-27); SECT63 3024 (checked 2026-09-28)
  32. 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.
    Idaho's values · engine step (compute_state_tax_detail). Sources (Social Security): unsourced: No official Idaho source could be fetched: tax.idaho.gov and legislature.idaho.gov (and every *.idaho.gov host tried) refuse connections from this host. No secondary source for Idaho's Social Security exemption was verified either.
  33. 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.
    Idaho's values · engine step (compute_state_tax_detail). Sources (Capital gains): 2025 Form 40 Instructions (archived) (checked 2026-09-28); 2025 Schedule D (Form 1040), Capital Gains and Losses (checked 2026-10-12)
  34. 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.socialSecurityGross when 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).
    Idaho's values · engine step (compute_state_tax_detail). Sources (Social Security): unsourced: No official Idaho source could be fetched: tax.idaho.gov and legislature.idaho.gov (and every *.idaho.gov host tried) refuse connections from this host. No secondary source for Idaho's Social Security exemption was verified either.
  35. 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).
    Idaho's values · engine step (state_tax_refundable_credits). Sources (Deductions, exemptions and credits): Individual income tax rate schedule (checked 2026-09-28); SECT63 3024 (checked 2026-09-28); 2025 Idaho Form 40 instructions (archived copy) (checked 2026-09-28); Rev. Proc. 2025-32 (2026 inflation adjustments) (checked 2026-10-12)

Rate schedule

Single

Taxable income fromtoRate
$0$4,8110%
$4,811and up5.3%

Married filing jointly

Taxable income fromtoRate
$0$9,6220%
$9,622and up5.3%

Head of household

Taxable income fromtoRate
$0$9,6220%
$9,622and up5.3%

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):

Deductions, exemptions and credits

  • Standard deduction (or the exemption the engine carries in its place): $16,100 single, $32,200 married filing jointly, $24,150 head of household.
  • The standard deduction includes $2,050 more for a single or head-of-household filer 65 or older, and $1,650 more for each spouse 65 or older on a married return.

Age 65+ subtractions and credits

  • The federal senior deduction is also taken against the state base: $6,000 for each taxpayer 65 or older, each reduced by 6% of income above $75,000 (single and head of household) or $150,000 (MFJ). Married couples filing separately get none.

Source review notes (what the sources do not state outright, or what the engine does not carry):

Social Security

Social Security benefits are fully exempt: none of the federally taxable amount enters the state base.

API value: socialSecurityRule: "exempt". The engine's input is the federally taxable amount; income tests use the sum of the income components as the adjusted-gross-income proxy.

Unsourced. No official Idaho source could be fetched: tax.idaho.gov and legislature.idaho.gov (and every *.idaho.gov host tried) refuse connections from this host. No secondary source for Idaho's Social Security exemption was verified either. Listed on the verification page.

IRA, 401(k) and private pensions

  • No exclusion: pension, annuity and IRA/401(k) distributions are taxed as ordinary income.

Unsourced. No official page states in terms that Idaho has no general retirement exclusion; Idaho Code 63-3022A (see Public pensions and Military retirement pay) lists the only retirement benefits Idaho deducts. Listed on the verification page.

Source review notes (what the sources do not state outright, or what the engine does not carry):

Public pensions

A public pension earned in service not covered by Social Security is subtracted: up to $49,824 ($74,736 on a joint return). Only a recipient 65 or older qualifies. The cap is reduced by the Social Security both spouses received. It is one deduction with the military retirement deduction: military pay excluded under that rule uses up the same cap. It applies only when the caller says the pension was not covered (pensionPublicSsCovered: false on the API); without that, no subtraction is given.

Otherwise 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):

Military retirement pay

  • Military retirement pay is exempt from age 62, up to $49,824; below that age up to $0, with $74,736 per joint return.
  • The military cap is reduced dollar for dollar by the taxpayer's Social Security.
  • Military pay the military rule does not exempt is pension income under the general retirement rules.
  • Rules are applied per taxpayer at that person's own age when the spouse's age is given. API value: rules.militaryRetirement.treatment: "capped_exclusion".

Roth conversions

A conversion is taxed as ordinary income in full. It does not draw any retirement-income exclusion.

Unsourced. No official Idaho source could be fetched: tax.idaho.gov and legislature.idaho.gov (and every *.idaho.gov host tried) refuse connections from this host. Listed on the verification page.

Capital gains

  • Net long-term gain is taxed as ordinary income.
  • Short-term gains are ordinary income.

Source review notes (what the sources do not state outright, or what the engine does not carry):

Blindness and disability

  • The standard deduction includes $2,050 more for a blind single or head-of-household filer and $1,650 more for each blind spouse on a married return. Age and blindness are separate: a person 65 or older and blind gets both amounts.
  • A disabled recipient of a qualifying public pension earned without Social Security coverage qualifies from 62.
  • A disabled military retiree qualifies for the military rule at any age.
  • The API applies these through its blind, disabled, spouse.blind and spouse.disabled fields; absent means false.

Part-year and nonresident returns

  • Part-year resident (Form 43): the tax on the state's own income (what was received while a resident, plus the state-source income while a nonresident), with the deductions and exemptions the form prorates scaled by its ratio.
  • Nonresident (Form 43): the tax on the state's own income (what was received while a resident, plus the state-source income while a nonresident), with the deductions and exemptions the form prorates scaled by its 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.
  • Prorated on a part-year return: the standard deduction.
  • Prorated on a nonresident return: the standard deduction.
  • 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.

SpousesIdaho's rule
One spouse a full-year resident, the other a part-year residenta joint part-year / nonresident return is required.
One spouse a full-year resident, the other a nonresidenta joint part-year / nonresident return is required.
One spouse a part-year resident, the other a nonresidenta joint part-year / nonresident return is required.
Both part-year residents, different resident periodsa joint part-year / nonresident return is required.
Both nonresidents, only one with income from the statea joint part-year / nonresident return is required.

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$1,942.33
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$2,812.53
Single, 60: $60,000 other ordinary income and a $50,000 Roth conversion$4,731.72
Married filing jointly, 66: $30,000 IRA, a $40,000 Roth conversion, $30,000 Social Security ($25,500 federally taxable)$692.53
Single, 58: $36,000 military retirement pay and $30,000 wages$491.72
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$567.98

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: $1,942.33
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: $2,812.53
Single, 60: $60,000 other ordinary income and a $50,000 Roth conversion: $4,731.72
Married filing jointly, 66: $30,000 IRA, a $40,000 Roth conversion, $30,000 Social Security ($25,500 federally taxable): $692.53
Single, 58: $36,000 military retirement pay and $30,000 wages: $491.72
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: $567.98

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 Idaho's law moves it. Rates and the rules themselves stay the 2026 ones (how projection works).

Amounts (engine fields)After 2026What 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)Indexed: CPI-U, calendar-year average of the preceding year over the 1998 average; not rounded (the statute states no rounding). The engine carries the 2025 figure (the latest published) for 2026, so a projection adds 1 year of indexing at the factor's average annual rate.Idaho Code 63-3024(2)-(3): 5.3% on taxable income over $2,500 ($5,000 joint/HOH/surviving spouse), the thresholds adjusted every year by the ratio of the prior calendar year's average CPI-U to the 1998 CPI-U; the statute states no rounding. The engine carries the TY2025 thresholds ($4,811 / $9,622).
  • Idaho Code § 63-3024 (Wayback copy) (Idaho Legislature, statute): Threshold indexing. Quoted: "multiply the last threshold amount by the percentage (the consumer price index for the calendar year immediately preceding the calendar year to which the adjusted threshold amount will apply divided by the consumer price index for calendar year 1998)"; "The consumer price index shall mean the consumer price index for all U.S. urban consumers". Checked 2026-09-30.
std_deduction_single, std_deduction_mfj, std_deduction_hohTied to an indexed federal amount: the federal basic standard deduction, IRC 63(c)(2)/63(c)(7) (chained CPI-U); the increase rounded down to a multiple of $50.These are the federal basic standard deduction amounts (IRC 63(c)(2); 2026 $16,100 single/MFS, $24,150 HOH, $32,200 joint), indexed from 2026 by the chained CPI with increases rounded down to $50 (IRC 63(c)(7)(B)(ii)). Idaho taxable income starts from federal taxable income under the Code as adopted each year (Idaho Code 63-3004), so the Idaho standard deduction is the federal one.
  • Idaho Code § 63-3004 (Wayback copy) (Idaho Legislature, statute): Idaho adopts the Internal Revenue Code as in effect on January 1, 2026 (updated each year). Quoted: "means the Internal Revenue Code as amended and in effect on the first day of January 2026". Checked 2026-09-30.
  • 26 U.S.C. 63 (taxable income defined) (Cornell LII (U.S. Code), federal): Federal standard deduction indexing and rounding. Quoted: "the $23,625 and $15,750 amounts in subparagraph (A) shall each be increased by an amount equal to"; "such increase shall be rounded to the next lowest multiple of $50.". Checked 2026-10-12.
  • Rev. Proc. 2025-32 (2026 inflation adjustments) (Internal Revenue Service, federal): 2026 federal standard deduction amounts. Quoted: "For taxable years beginning in 2026, the standard deduction amounts under § 63(c)(2) are as follows:". Checked 2026-10-12.
std_deduction_aged_add_unmarried, std_deduction_aged_add_married, blind_std_add_unmarried, blind_std_add_marriedTied to an indexed federal amount: the federal additional standard deduction for age/blindness, IRC 63(f), indexed under IRC 63(c)(4) (chained CPI-U); the increase rounded down to a multiple of $50.These are the federal additional standard deduction amounts for age 65+/blindness (IRC 63(f); 2026 $1,650 married, $2,050 unmarried), indexed under IRC 63(c)(4) by the chained CPI, increases rounded down to $50 (IRC 1(f)(7)(A)).
  • 26 U.S.C. 63 (taxable income defined) (Cornell LII (U.S. Code), federal): 63(c)(4) indexes the subsection (f) amounts. Quoted: "each dollar amount contained in paragraph (2)(B), (2)(C), or (5) or subsection (f) shall be increased by an amount equal to". Checked 2026-10-12.
  • 26 U.S.C. 1 (tax imposed) (Cornell LII (U.S. Code), federal): 1(f)(7)(A) rounds a 63(c)(4) increase down to $50. Quoted: "If any increase determined under paragraph (2)(A), section 63(c)(4), section 68(b)(2)". Checked 2026-10-12.
  • Rev. Proc. 2025-32 (2026 inflation adjustments) (Internal Revenue Service, federal): 2026 amounts. Quoted: "deduction amount under § 63(f) for the aged or the blind is $1,650". Checked 2026-10-12.
fed_senior_deductionEnacted schedule: 2027: $6,000; 2028: $6,000; 2029: $0; held at the 2029 value after 2029.The federal senior deduction of IRC 151(d)(5)(C) is $6,000 per qualified individual for taxable years beginning before January 1, 2029, and nothing after: $6,000 in 2027 and 2028, $0 from 2029.
  • 26 U.S.C. 151 (allowance of deductions for personal exemptions) (Cornell LII (U.S. Code), federal): The deduction exists only for taxable years beginning before 2029. Quoted: "In the case of a taxable year beginning before January 1, 2029, there shall be allowed a deduction in an amount equal to $6,000". Checked 2026-10-12.
fed_senior_phaseout_single, fed_senior_phaseout_mfjFixed in law: held at the rules-year amount in every later year.The federal senior deduction phases out above modified AGI of $75,000 ($150,000 joint); these amounts are fixed in IRC 151(d)(5)(C)(iii) with no inflation adjustment (and the deduction itself ends after 2028).
military_cap, military_cap_mfj, noncov_pension_cap_single, noncov_pension_cap_mfjIndexed: maximum annual Social Security benefit at full retirement age (single; joint = worker plus spousal benefit), SSA COLA; not rounded (the statute states no rounding).Idaho Code 63-3022A(2): the retirement benefits deduction is capped at the maximum Social Security benefit payable to a person attaining full retirement age in the tax year (single) and the maximum worker-plus-spouse benefit (joint, 1.5x), so it moves with the SSA maximum benefit (COLA under section 215). Engine 1.10.0 carries (it carried the TY2025 $48,216 / $72,324 before) the 2026 amounts ($49,824 / $74,736: the 2026 maximum benefit at full retirement age, $4,152 a month), so the projection indexes from 2026.
  • Idaho Code § 63-3022A (Wayback copy) (Idaho Legislature, statute): Cap tied to the SSA maximum benefit. Quoted: "an amount equal to maximum social security benefits payable for the tax year to a person attaining full retirement age in the tax year"; "including adjustments to be made based on consumer price index adjustments provided in section 215 of the social security act". Checked 2026-10-12.
military_min_age, noncov_pension_min_age, noncov_pension_disabled_min_ageAttained age: the same age in every year.The deduction requires age 65, or 62 if disabled (civil-service / police / fire), and for military retirees age 62 by year end: fixed attained ages.
  • Idaho Code § 63-3022A (Wayback copy) (Idaho Legislature, statute): Ages 65 / 62. Quoted: "If such individual has either attained age sixty-five (65) years or has attained age sixty-two (62) years and is classified as disabled"; "Has attained the age of sixty-two (62) years by the end of the tax year". Checked 2026-10-12.
flat_tax_per_returnFixed in law: held at the rules-year amount in every later year.Idaho Code 63-3082: $10 per required return (joint = one); fixed.
  • Idaho Code § 63-3082 (Wayback copy) (Idaho Legislature, statute): Fixed $10. Quoted: "Every person required to file an income tax return shall pay a tax of ten dollars ($10.00).". Checked 2026-09-30.
filing_threshold_mfsFixed in law: held at the rules-year amount in every later year.The federal gross-income filing threshold on a married-filing-separately return is $5 at any age (tied to the exemption amount, which is zero), not an indexed amount.
  • Publication 501 (Internal Revenue Service, federal): MFS threshold $5. Quoted: "married filing separately any age $5". Checked 2026-10-12.
cap_loss_limit, cap_loss_limit_mfsFixed 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.
  • 26 U.S.C. 1211 (limitation on capital losses) (Cornell LII (U.S. Code), federal): The capital-loss deduction against ordinary income is a fixed $3,000 ($1,500 MFS); section 1211 contains no inflation adjustment. Quoted: "$3,000 ($1,500 in the case of a married individual filing a separate return), or". Checked 2026-10-12.
id-grocery-credit (a table held in code)Fixed in law: held at the rules-year amount in every later year.Idaho Code 63-3024A sets the grocery credit per person; it changes only by legislation (no indexing clause); $155 for 2025.
  • Form 40 Instructions 2025 (Idaho Individual Income Tax) (Idaho State Tax Commission, instructions): Food (grocery) Tax Credit (Form 40 line 43) - refundable Quoted: "The credit is either $155 each for you, your spouse,"; "of sales tax paid during the year (up to $250 each)". Checked 2026-10-12.

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

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 backend/tests/test_state_worksheets_1.c replays the 2025 Idaho Form 40 (with the 2026 federal standard-deduction figures Idaho adopts) line by line: Form 39R Part B line 7 (taxable Social Security) and line 8 (Retirement Benefits Deduction for military and CSRS, per-return cap reduced by Social Security), the standard deduction worksheet with the 65+ amounts, line 18 federal Schedule 1-A senior deduction and its phase-out, and the line 20 tax worksheet.