Federal tax engine: later tax years

fed-ordinary-brackets: indexed

ordinary brackets (all statuses) (§1(f)(3), §1(f)(7), §1(j)(3)(B)): 2026 see rule ord_mfj etc.. C-CPI-U, §1(f)(3) cost-of-living adjustment; §1(j)(3)(B): 'calendar year 2017' base for bracket edges above 12% end / above 22% begin, else 2016 base

Statute: §1(f)(3), §1(f)(7), §1(j)(3)(B). Index: C-CPI-U.

Rounding: increase rounded to next lowest multiple of $50; $25 for MFS and for unmarried other than HOH/surviving spouse (§1(f)(7)(B) via §1(j)(3)(B)(ii)) (the increase).

The prompt's '$25' example is the MFS/single variant; the general rule is $50.

• 26 U.S.C. 1 checked 2026-10-12
  if any increase determined under paragraph (2)(a), section 63(c)(4), section 68(b)(2) [1] or section 151(d)(4) is not a multiple of $50, such increase shall be rounded to the next lowest multiple of $50; not over $19,050 10% of taxable income. over $19,050 but not over $77,400; over $165,000 but not over $315,000 $28,179, plus 24% of the excess over $165,000. over $315,000 but not over $400,000; over $400,000 but not over $600,000 $91,379, plus 35% of the excess over $400,000; not over $13,600 10% of taxable income. over $13,600 but not over $51,800; over $157,500 but not over $200,000 $30,698, plus 32% of the excess over $157,500. over $200,000 but not over $500,000 $44,298; not over $9,525 10% of taxable income. over $9,525 but not over $38,700 $952.50; over $38,700 but not over $82,500 $4,453.50, plus 22% of the excess over $38,700. over $82,500 but not over $157,500 $14,089.50; over $200,000 but not over $300,000 $45,689.50, plus 35% of the excess over $200,000. over $300,000 $80,689.50; solely for purposes of determining the dollar amounts at which any rate bracket higher than 12 percent ends and at which any rate bracket higher than 22 percent begins; subsection (f)(7)(b) shall apply to any unmarried individual other than a surviving spouse or head of household; shall be applied by substituting "$25" for "$50" each place it appears; the c-cpi-u for any calendar year is the average of the c-cpi-u as of the close of the 12-month period ending on august 31 of such calendar year

fed-standard-deduction: indexed

basic standard deduction (§63(c)(7)(B)(ii)): 2026 16,100 / 32,200 / 24,150. C-CPI-U, §1(f)(3) cost-of-living adjustment, base 2024 ($15,750 / $23,625 per §63(c)(7)(A))

Statute: §63(c)(7)(B)(ii). Index: C-CPI-U.

Rounding: increase rounded to next lowest multiple of $50 (the increase).

• 26 U.S.C. 63 checked 2026-10-12
  determined by substituting "2024" for "2016" in subparagraph (a)(ii) thereof. if any increase under this clause is not a multiple of $50, such increase shall be rounded to the next lowest multiple of $50; by substituting "$23,625" for "$4,400" in subparagraph (b), and (ii) by substituting "$15,750" for "$3,000" in subparagraph (c); 200 percent of the dollar amount in effect under subparagraph (c) for the taxable year in the case of

fed-63f-aged-blind: indexed

§63(f) additional aged/blind (§63(c)(4), §63(f)): 2026 1,650 married / 2,050 unmarried. C-CPI-U, §1(f)(3) cost-of-living adjustment, base 1987 (§63(c)(4))

Statute: §63(c)(4), §63(f). Index: C-CPI-U.

Rounding: next lowest $50 (§1(f)(7)(A) names section 63(c)(4); the MFS $25 rule excludes 63(c)(4)) (the increase).

federal_tax.c:651 scales the blind amount by year_factor without the $50 rounding.

• 26 U.S.C. 63 checked 2026-10-12
  "calendar year 1987" in the case of the dollar amounts contained in paragraph (2)(b), (2)(c), or (5)(a) or subsection (f); the taxpayer shall be entitled to an additional amount of $600; shall be applied by substituting "$750" for "$600"

fed-ltcg-breakpoints: indexed

LTCG 0% / 15% maximum amounts (§1(j)(5)(C)): 2026 see rule ltcg. C-CPI-U, §1(f)(3) cost-of-living adjustment, base 2017

Statute: §1(j)(5)(C). Index: C-CPI-U.

Rounding: next lowest multiple of $50 (the increase).

• 26 U.S.C. 1 checked 2026-10-12
  determined by substituting "calendar year 2017" for "calendar year 2016" in subparagraph (a)(ii) thereof. if any increase under this subparagraph is not a multiple of $50, such increase shall be rounded to the next lowest multiple of $50. (6) section 15; in the case of a joint return or surviving spouse, $77,200, (ii) in the case of an individual who is a head of household (as defined in section 2(b)), $51,700; in the case of a joint return or surviving spouse, $479,000; in the case of an individual who is the head of a household (as defined in section 2(b)), $452,400, (iii) in the case of any other individual (other than an estate or trust), $425,800

fed-niit-thresholds: fixed in law

NIIT thresholds 250k/200k/125k (§1411(b)): 2026 250,000 / 200,000 / 125,000. No indexing provision.

Statute: §1411(b).

No inflation clause in §1411 (existing rule niit).

• 26 U.S.C. 1411 checked 2026-10-12
  in any other case, $200,000

fed-addl-medicare-thresholds: fixed in law

Additional Medicare thresholds (§3101(b)(2), §1401(b)(2)): 2026 250,000 / 200,000 / 125,000. No indexing provision.

Statute: §3101(b)(2), §1401(b)(2).

• 26 U.S.C. 3101 checked 2026-10-12
  a tax equal to 0.9 percent of wages which are received with respect to employment
• 26 U.S.C. 3102 checked 2026-10-12
  subsection (a) shall only apply to the extent to which the taxpayer receives wages from the employer in excess of $200,000

fed-ss-benefit-thresholds: fixed in law

SS benefit base / adjusted base (§86(c)): 2026 25k/32k/0; 34k/44k/0. No indexing provision.

Statute: §86(c).

• 26 U.S.C. 86 checked 2026-10-12
  (a) except as otherwise provided in this paragraph, $25,000, (b) $32,000 in the case of a joint return, and (c) zero

fed-capital-loss-limit: fixed in law

capital loss limit (§1211(b)): 2026 3,000 / 1,500 MFS. No indexing provision.

Statute: §1211(b).

• 26 U.S.C. 1211 checked 2026-10-12
  the lower of- (1) $3,000 ($1,500 in the case of a married individual filing a separate return)

fed-oasdi-wage-base: wage-indexed

OASDI wage base (42 U.S.C. 430(b)): 2026 184,500. AWI ratio vs 1992 x $60,600 (42 USC 430(b)); only moves in a COLA year

Statute: 42 U.S.C. 430(b). Index: AWI (42 U.S.C. 430(b)): national average wage index ratio vs 1992 times $60,600; changes only in a year with a benefit COLA.

Rounding: nearest $300 (x.5 -> up) (the amount).

SSA publishes it each October/November (FR notice); a projection must use the AWI path, not CPI.

• 42 U.S.C. 430 checked 2026-10-12
  with such product, if not a multiple of $300, being rounded to the next higher multiple of $300 where such product is a multiple of $150 but not of $300 and to the nearest multiple of $300 in any other case; (1) $60,600, and (2) the ratio of (a) the national average wage index

fed-earnings-test-exempt: wage-indexed

earnings-test exempt amounts (42 U.S.C. 403(f)(8)(B)): 2026 24,480 / 65,160. AWI ratio vs 1992 (lower) / 2000 (higher), monthly amounts

Statute: 42 U.S.C. 403(f)(8)(B). Index: AWI (42 U.S.C. 403(f)(8)(B)): monthly exempt amounts, ratio vs 1992 (lower) / 2000 (higher).

Rounding: monthly amount to nearest $10 (x5 -> up); annual = 12x (the monthly amount).

• 42 U.S.C. 403 checked 2026-10-12
  with such product, if not a multiple of $10, being rounded to the next higher multiple of $10 where such product is a multiple of $5 but not of $10; for each month of any taxable year ending after 2001 and before 2003, $2,500.00
• Exempt amounts under the earnings test, 1975-1999 checked 2026-10-12
  1994 8,040 11,160

fed-se-floor: fixed in law

SE $400 floor (§1402(b)(2)): 2026 400. No indexing provision.

Statute: §1402(b)(2).

• 26 U.S.C. 1402 checked 2026-10-12
  if such net earnings for the taxable year are less than $400

fed-se-rates: fixed in law

SE rates 12.4% / 2.9%, 92.35% factor (§1401(a)-(b), §1402(a)(12)): 2026 0.124 / 0.029 / 0.9235. No indexing provision.

Statute: §1401(a)-(b), §1402(a)(12).

A rate, not a dollar amount: it never moves.

• 26 U.S.C. 1401 checked 2026-10-12
  a tax equal to 12.4 percent of the amount of the self-employment income

fed-ftc-904j-ceiling: fixed in law

FTC no-1116 election ceiling (§904(j)(2)(B)): 2026 300 / 600 joint. No indexing provision.

Statute: §904(j)(2)(B).

• 26 U.S.C. 904 checked 2026-10-12
  does not exceed $300 ($600 in the case of a joint return)

fed-amt-exemption: indexed

AMT exemption (§55(d)(4)(B)): 2026 140,200 / 90,100 / 70,100. C-CPI-U, §1(f)(3) cost-of-living adjustment, base 2017 for $109,400 / $70,300; MFS = 50% of MFJ

Statute: §55(d)(4)(B). Index: C-CPI-U.

Rounding: nearest multiple of $100 (the amount).

• 26 U.S.C. 55 checked 2026-10-12
  "calendar year 2017", in the case of the $109,400 amount in subparagraph (a)(i)(i) and the $70,300 amount in subparagraph (a)(i)(ii); by substituting "$109,400" for "$78,750" in subparagraph (a), and (ii) by substituting "$70,300" for "$50,600" in subparagraph (b); any increased amount determined under clause (i) shall be rounded to the nearest multiple of $100

fed-amt-phaseout-threshold: indexed

AMT phase-out threshold (§55(d)(4)(A)(ii), (B) as amended by P.L. 119-21 §70107): 2026 1,000,000 MFJ / 500,000 other & MFS. C-CPI-U, §1(f)(3) cost-of-living adjustment, base 2025, first adjusted in 2027 (not adjusted before 2027); unmarried and MFS = 50% of the MFJ amount

Statute: §55(d)(4)(A)(ii), (B) as amended by P.L. 119-21 §70107. Index: C-CPI-U.

Rounding: nearest multiple of $100 (the amount).

Phase-out rate 50% (was 25%) from 2026.

• 26 U.S.C. 55 checked 2026-10-12
  (2026, in the case of the $1,000,000 amount in subparagraph (a)(ii)(i)); by substituting "$1,000,000" for "$150,000" in subparagraph (a), (ii) by substituting "50 percent of the dollar amount applicable under subparagraph (a)" for "$112,500"; "calendar year 2025", in the case of the $1,000,000 amount in subparagraph (a)(ii)(i)

fed-amt-28-breakpoint: indexed

AMT 28% breakpoint (§55(d)(3)): 2026 244,500 / 122,250 MFS. C-CPI-U, §1(f)(3) cost-of-living adjustment, base 2011 ($175,000)

Statute: §55(d)(3). Index: C-CPI-U.

Rounding: nearest multiple of $100 (the amount).

• 26 U.S.C. 55 checked 2026-10-12
  determined by substituting "calendar year 2011" for "calendar year 2016" in subparagraph (a)(ii) thereof; 26 percent of so much of the taxable excess as does not exceed $175,000

fed-qbi-threshold: indexed

QBI threshold (§199A(e)(2)(B)): 2026 201,750 / 201,775 MFS / 403,500 MFJ. C-CPI-U, §1(f)(3) cost-of-living adjustment, base 2017 ($157,500; joint 200%)

Statute: §199A(e)(2)(B). Index: C-CPI-U.

Rounding: as §1(f)(7): next lowest $50 ($25 MFS) (the increase).

Unchanged by OBBBA.

• 26 U.S.C. 199A checked 2026-10-12
  the amount of any increase under the preceding sentence shall be rounded as provided in section 1(f)(7); means $157,500 (200 percent of such amount in the case of a joint return)

fed-qbi-phase-in-range: fixed in law

QBI phase-in range (§199A(b)(3)(B), (d)(3)): 2026 75,000 / 150,000 joint. No indexing provision.

Statute: §199A(b)(3)(B), (d)(3).

• 26 U.S.C. 199A checked 2026-10-12
  plus $75,000 ($150,000 in the case of a joint return)

fed-qbi-minimum: indexed

QBI minimum deduction / active-QBI floor (§199A(i)(3)): 2026 400 / 1,000. C-CPI-U, §1(f)(3) cost-of-living adjustment, base 2025, from taxable years beginning after 2026

Statute: §199A(i)(3). Index: C-CPI-U.

Rounding: nearest multiple of $5 (the increase).

• 26 U.S.C. 199A checked 2026-10-12
  if any increase under this paragraph is not a multiple of $5, such increase shall be rounded to the nearest multiple of $5

fed-salt-cap: scheduled

SALT cap (§164(b)(7)(A)): 2026 40,400 (2026). 101% of prior year 2027-2029; $10,000 from 2030

Statute: §164(b)(7)(A).

Statute gives no rounding; 2027 = 40,804 by arithmetic (not quoted).

• 26 U.S.C. 164 checked 2026-10-12
  101 percent of the dollar amount in effect under this subparagraph for taxable years beginning in the preceding calendar year, and (iv) in the case of any taxable year beginning after calendar year 2029, $10,000

fed-salt-phasedown-threshold: scheduled

SALT phase-down threshold (§164(b)(7)(B)): 2026 505,000 (2026). 101% of prior year after 2026; phase-down applies only to years before 2030

Statute: §164(b)(7)(B).

• 26 U.S.C. 164 checked 2026-10-12
  in the case of any taxable year beginning in calendar year 2026, $505,000

fed-salt-floor: fixed in law

SALT floor (§164(b)(7)(B)(iii)): 2026 10,000. No indexing provision.

Statute: §164(b)(7)(B)(iii).

• 26 U.S.C. 164 checked 2026-10-12
  shall not result in the applicable limitation amount being less than $10,000

fed-senior-deduction: scheduled

senior deduction (§151(d)(5)(C)): 2026 6,000; phase-out 6% over 75,000 / 150,000. none (fixed amount and thresholds)

Statute: §151(d)(5)(C).

Fixed in law AND expires after 2028.

• 26 U.S.C. 151 checked 2026-10-12
  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

fed-tips-cap: scheduled

tips cap (§224(b), (h)): 2026 25,000; phase-out 150k/300k. No indexing provision.

Statute: §224(b), (h).

Fixed amount; expires after 2028.

• 26 U.S.C. 224 checked 2026-10-12
  no deduction shall be allowed under this section for any taxable year beginning after december 31, 2028

fed-overtime-cap: scheduled

overtime cap (§225(b), (g)): 2026 12,500 / 25,000 joint; phase-out 150k/300k. No indexing provision.

Statute: §225(b), (g).

Fixed amount; expires after 2028.

• 26 U.S.C. 225 checked 2026-10-12
  shall not exceed $12,500 ($25,000 in the case of a joint return)

fed-170p-cap: fixed in law

§170(p) non-itemizer charity (§170(p)): 2026 1,000 / 2,000 joint. No indexing provision.

Statute: §170(p).

• 26 U.S.C. 170 checked 2026-10-12
  not in excess of 1,000 ($2,000 in the case of a joint return)

fed-charity-floor-rate: fixed in law

charity 0.5% floor (§170(b)(1)(I)): 2026 0.5% of contribution base. No indexing provision.

Statute: §170(b)(1)(I).

A rate, not a dollar amount: it never moves.

• 26 U.S.C. 170 checked 2026-10-12
  exceeds 0.5 percent of the taxpayer's contribution base for the taxable year

fed-irmaa-floors: indexed

IRMAA income floors (42 U.S.C. 1395r(i)(5)): 2026 109k..500k single / 218k..750k MFJ. CPI-U (not chained) Sept-Aug average vs Aug 2006 (Aug 2018 base for 2020+); the $500,000 tier is frozen, then indexed after 2027 from Aug 2026

Statute: 42 U.S.C. 1395r(i)(5). Index: CPI-U (all items, U.S. city average; not chained), the average of the 12 months ending August of the year before; base the 12 months ending August 2018 (tiers 1-4) and August 2026 (the $500,000 tier, held at $500,000 through 2027).

Rounding: nearest multiple of $1,000 (the amount).

joint returns: twice the individual amounts, 150 percent of the $500,000 tier (1395r(i)(3)(C)(ii)); a married individual filing separately who lived with the spouse: each individual amount reduced by the individual threshold (1395r(i)(3)(C)(iii)), so the surcharge starts above the threshold and the top tier at $500,000 less it.

Premium-year floors apply to MAGI from 2 years earlier.

• 42 U.S.C. 1395r checked 2026-10-12
  if any dollar amount after being increased under subparagraph (a) or (c) is not a multiple of $1,000, such dollar amount shall be rounded to the nearest multiple of $1,000; $80,000 (or, beginning with 2018, $85,000); more than $85,000 but not more than $107,000 35 percent more than $107,000 but not more than $133,500 50 percent more than $133,500 but not more than $160,000 65 percent more than $160,000 but less than $500,000 80 percent at least $500,000 85 percent; twice the dollar amounts otherwise applicable under clause (i) for the calendar year; shall be applied by substituting dollar amounts which are 150 percent of such dollar amounts for the calendar year; by reducing each of the dollar amounts otherwise applicable under such clause for the calendar year by the threshold amount for such year applicable to an unmarried individual; (or, in the case of a calendar year beginning with 2020, august 2018); subparagraph (a) shall not apply with respect to each dollar amount in paragraph (3) of $500,000; in the case of any calendar year beginning after 2027, each dollar amount in paragraph (3) of $500,000 shall be increased; for the 12-month period ending with august 2026

fed-qcd-limits: indexed

QCD annual limit / split-interest (§408(d)(8)(G)): 2026 111,000 / 55,000. C-CPI-U, §1(f)(3) cost-of-living adjustment, base 2022, taxable years after 2023

Statute: §408(d)(8)(G). Index: C-CPI-U.

Rounding: nearest multiple of $1,000 (the amount).

rmd.c:127 and federal_tax.c:1039 round to nearest $1,000 - consistent with the statute.

• 26 U.S.C. 408 checked 2026-10-12
  if any dollar amount increased under clause (i) is not a multiple of $1,000, such dollar amount shall be rounded to the nearest multiple of $1,000; which does not exceed $100,000 shall not be includible in gross income; with respect to which an election under this subparagraph is made does not exceed $50,000; determined by substituting "calendar year 2022" for "calendar year 2016" in subparagraph (a)(ii) thereof

fed-senior-phaseout-thresholds: fixed in law

senior phase-out thresholds (§151(d)(5)(C)(iii)): 2026 75,000 / 150,000. No indexing provision.

Statute: §151(d)(5)(C)(iii).

• 26 U.S.C. 151 checked 2026-10-12
  reduced (but not below zero) by 6 percent of so much of the taxpayer's modified adjusted gross income as exceeds $75,000

fed-ctc: indexed

CTC per child (§24(i)(2)-(3)): 2026 2,200. C-CPI-U, §1(f)(3) cost-of-living adjustment, base 2024, taxable years after 2025

Statute: §24(i)(2)-(3). Index: C-CPI-U.

Rounding: next lowest multiple of $100 (the increase).

Engine 2.1.0 (fed/2.1): Schedule 8812 in backend/src/federal_tax.c (FedWorkParams.ctc_per_child); frontend/js/calc/constants-2026.js also carries it for the site pages. Provenance rules ctc, ctc_8812.

• 26 U.S.C. 24 checked 2026-10-12
  if any increase under this subsection is not a multiple of $100, such increase shall be rounded to the next lowest multiple of $100; the $2,200 amount in subsection (h)(2) shall be increased by an amount equal to

fed-6654-110pct-trigger: fixed in law

estimated-tax 110% AGI trigger (§6654(d)(1)(C)): 2026 150,000 / 75,000 MFS. No indexing provision.

Statute: §6654(d)(1)(C).

• 26 U.S.C. 6654 checked 2026-10-12
  exceeds $150,000, clause (ii) of subparagraph (b) shall be applied by substituting "110 percent" for "100 percent"

fed-6654-de-minimis: fixed in law

estimated-tax penalty de minimis (§6654(e)(1)): no addition to tax when the year's tax less withholding is under $1,000. No indexing provision.

Statute: §6654(e)(1).

• 26 U.S.C. 6654 checked 2026-10-12
  reduced by the credit allowable under section 31, is less than $1,000

fed-tax-table-ceiling: not established

Tax Table ceiling (§3 (tables authorised), i1040 line 16): 2026 100,000. administrative (IRS instructions), not statutory

Statute: §3 (tables authorised), i1040 line 16.

Administrative. §3 lets the Secretary prescribe tables but sets no ceiling. Not indexed in practice (it has stayed $100,000), but no source commits to that.

• Instructions for Form 1040 (2025) checked 2026-10-12
  if your taxable income is less than $100,000, you must use the tax table

fed-tips-overtime-phaseout: fixed in law

tips and overtime deduction phase-out thresholds (§224(b)(2), §225(b)(2)): $150,000 / $300,000 joint, fixed amounts (the deductions themselves end after 2028: rules fed-tips-cap, fed-overtime-cap)

Statute: §224(b)(2), §225(b)(2).

• 26 U.S.C. 224 checked 2026-10-12
  by which the taxpayer's modified adjusted gross income exceeds $150,000 ($300,000 in the case of a joint return)

fed-ftc-adjustment-exception: fixed in law

Form 1116 adjustment exception: no rate-differential adjustment when foreign capital-gain distributions plus foreign qualified dividends are under $20,000 (i1116). An instructions figure the statute does not index; held at $20,000.

Statute: §904(b)(2)(B) (the instructions' exception).

Administrative: printed in the Form 1116 instructions; no statute indexes it. Held at $20,000 in both modes.

• Instructions for Form 1116 checked 2026-10-12
  the amount of your foreign source capital gain distributions plus the amount of your foreign source qualified dividends is less than $20,000

fed-pal-allowance: fixed in law

Rental real estate special allowance (§469(i)(2), (3)(A), (5)(A)): 2026 25,000, reduced by 50% of MAGI over 100,000; married filing separately and living apart all year 12,500 / 50,000. No indexing provision.

Statute: §469(i)(2), (3)(A), (5)(A).

Fixed since the Tax Reform Act of 1986: §469 has no inflation clause. The 50 percent phase-out rate is a rate (FedWorkParams.pal_phaseout_rate, not a dollar amount). Provenance rules passive_loss_469, form_8582.

• 26 U.S.C. 469 checked 2026-10-12
  The aggregate amount to which paragraph (1) applies for any taxable year shall not exceed $25,000.; by 50 percent of the amount by which the adjusted gross income of the taxpayer for the taxable year exceeds $100,000; (i) "$12,500" for "$25,000" each place it appears, (ii) "$50,000" for "$100,000" in paragraph (3)(A)

fed-elderly-credit: fixed in law

Credit for the elderly or the disabled (§22(c)(2)(A), (d)): 2026 initial amounts 5,000 (single, or joint with one qualified spouse) / 7,500 (joint, both qualified) / 3,750 (married filing separately); AGI thresholds 7,500 / 10,000 / 5,000. No indexing provision.

Statute: §22(c)(2)(A), (d).

Unchanged since 1983: §22 has no inflation clause. The 15 percent credit rate is a rate (FedWorkParams.elderly_rate). Provenance rule elderly_credit_22.

• 26 U.S.C. 22 checked 2026-10-12
  (i) $5,000 in the case of a single individual, or a joint return where only one spouse is a qualified individual, (ii) $7,500 in the case of a joint return where both spouses are qualified individuals, or (iii) $3,750 in the case of a married individual filing a separate return; (1) $7,500 in the case of a single individual, (2) $10,000 in the case of a joint return, or (3) $5,000 in the case of a married individual filing a separate return

fed-savers-cap: scheduled

Saver's credit contribution cap (§25B(a), (d)(1)(B)): 2026 2,000 per person. From 2027 retirement contributions no longer count (§25B(d)(1)(B) as amended by Pub. L. 119-21 §70116(a)); the cap is 0 for the engine's (retirement) contributions.

Statute: §25B(a), (d)(1)(B).

§25B(d)(1)(B) counts IRA contributions and elective deferrals only "in the case of any taxable year beginning before January 1, 2027"; SECURE 2.0 §103 (26 U.S.C. 6433) replaces them with the Saver's Match from 2027. The credit itself continues for ABLE contributions by the designated beneficiary, with a $2,100 cap from 2027 (§70116(b)); ABLE contributions are not an engine input. Provenance rule savers_credit_25b.

• 26 U.S.C. 25B checked 2026-10-12
  as do not exceed $2,000; in the case of any taxable year beginning before January 1, 2027- (i) the amount of the qualified retirement contributions (as defined in section 219(e)) made by the eligible individual; applicable to taxable years beginning after Dec. 31, 2026, subsection (a) of this section is amended by striking "$2,000" and inserting "$2,100"

fed-savers-agi: indexed

Saver's credit AGI tops (§25B(b)): 2026 joint 48,500 (50%) / 52,500 (20%) / 80,500 (10%); head of household 75% and all others 50% of the joint amounts. C-CPI-U, §1(f)(3) cost-of-living adjustment, base 2005 for $30,000 / $32,500 / $50,000, increase rounded to the nearest $500

Statute: §25B(b)(1)-(3). Index: C-CPI-U.

Rounding: nearest multiple of $500 (the increase).

§25B(b)(2): the head-of-household and other amounts are 75% / 50% of the joint amounts AS ADJUSTED (Notice 2025-67: 36,375 = 0.75 x 48,500), so they are derived, not separately rounded. A qualifying surviving spouse is in the 'others' column (Form 8880). Indexed after 2026 as the statute says; from 2027 the credit applies only to ABLE contributions, so the engine's credit is 0 there (rule fed-savers-cap). Engine layout: FedWorkParams.savers_agi[3 x s + b], s = joint / head of household / other, b = the 50% / 20% / 10% band top.

• 26 U.S.C. 25B checked 2026-10-12
  determined by substituting "calendar year 2005" for "calendar year 2016" in subparagraph (A)(ii) thereof. Any increase determined under the preceding sentence shall be rounded to the nearest multiple of $500.; a dollar amount equal to 75 percent of such dollar amount
• Notice 2025-67: 2026 retirement plan limitations checked 2026-10-12
  married taxpayers filing a joint return is increased from $47,500 to $48,500; the limitation under section 25B(b)(1)(B) is increased from $51,000 to $52,500; is increased from $79,000 to $80,500; the limitation under section 25B(b)(1)(B) is increased from $38,250 to $39,375; the limitation under section 25B(b)(1)(B) is increased from $25,500 to $26,250

fed-eitc-amounts: indexed

EITC earned income and phaseout amounts (§32(b)(2)): 2026 earned income amounts 8,680 / 13,020 / 18,290 / 18,290 (0 / 1 / 2 / 3+ children); phaseout begins 10,860 / 23,890 (others), 18,140 / 31,160 (joint). C-CPI-U, §1(f)(3), base 1995 for the (b)(2)(A) amounts and 2008 for the $5,000 joint increase, the sum rounded to the nearest $10

Statute: §32(b)(2), (j). Index: C-CPI-U.

Rounding: nearest multiple of $10 (the joint amount after the (b)(2)(B) increase) (the amount).

§32(j)(2)(A) rounds the (b)(2)(A) amount 'after being increased under subparagraph (B)': the joint phaseout amount is ONE rounded amount, 11,610 x I(2025)/I(1995) + 5,000 x I(2025)/I(2008) (2026: 23,885.33 + 7,275.29 = 31,160.61 -> 31,160; childless 18,137.86 -> 18,140, not 10,860 + 7,280 or + 7,270). Both terms move by the same factor after 2026, so each joint amount is carried as a 1995-base amount whose base_amount is the statute amount plus 5,000 x I(1995) / I(2008) (the CPI-U Sep-Aug averages of the registry's months; I(1995) / I(2008) = 0.70726...). The maximum credit (credit percentage x earned income amount) and the completed phaseout amount (threshold + maximum / phaseout percentage) follow from these and are not separate parameters. Provenance rules eitc (Rev. Proc. 2025-32 §4.06), eitc_pct, eitc_rules_32. Engine layout: FedWorkParams.eitc_threshold[4 x j + k], j = 0 joint / 1 other, k = qualifying children 0-3. FedWorkParams.eitc_max (the credit percentage x the earned income amount, rounded to the dollar as Rev. Proc. 2025-32 prints it) and eitc_completed (threshold + maximum / phaseout percentage, rounded to the dollar) are not separate amounts of the law: scripts/check_federal_tax_indexing.mjs re-derives both from these amounts and the engine's §32(b)(1) percentages, and the projection must recompute them the same way.

• 26 U.S.C. 32 checked 2026-10-12
  in the case of amounts in subsection (b)(2)(A), "calendar year 1995" for "calendar year 2016", (ii) in the case of the $5,000 amount in subsection (b)(2)(B), "calendar year 2008" for "calendar year 2016"; If any dollar amount in subsection (b)(2)(A) (after being increased under subparagraph (B) thereof), after being increased under paragraph (1), is not a multiple of $10, such dollar amount shall be rounded to the nearest multiple of $10.; 1 qualifying child $6,330 $11,610 2 or more qualifying children $8,890 $11,610 No qualifying children $4,220 $5,280; the phaseout amount determined under subparagraph (A) shall be increased by $5,000
• Rev. Proc. 2025-32: 2026 inflation-adjusted items checked 2026-10-12
  Earned Income Amount $13,020 $18,290 $18,290 $8,680 Maximum Amount of Credit $4,427 $7,316 $8,231 $664; Threshold Phaseout Amount (Married Filing Jointly) $31,160 $31,160 $31,160 $18,140; Threshold Phaseout Amount (All other filing statuses) $23,890 $23,890 $23,890 $10,860

fed-eitc-investment-limit: indexed

EITC disqualified (investment) income limit (§32(i)(1)): 2026 12,200. C-CPI-U, §1(f)(3), base 2020 for $10,000, rounded down to a multiple of $50

Statute: §32(i)(1), (j)(1)(B)(iii), (j)(2)(B). Index: C-CPI-U.

Rounding: next lowest multiple of $50 (the amount).

Provenance rules eitc, eitc_rules_32 (Pub 596 Worksheet 1).

• 26 U.S.C. 32 checked 2026-10-12
  the aggregate amount of disqualified income of the taxpayer for the taxable year exceeds $10,000; in the case of the $10,000 amount in subsection (i)(1), "calendar year 2020" for "calendar year 2016"; such amount shall be rounded to the next lowest multiple of $50
• Rev. Proc. 2025-32: 2026 inflation-adjusted items checked 2026-10-12
  aggregate amount of certain investment income exceeds $12,200

fed-ctc-refundable: indexed

Refundable child tax credit per child (§24(h)(5), (i)(1)): 2026 1,700. C-CPI-U, §1(f)(3), base 2017 for $1,400, increase rounded down to a multiple of $100

Statute: §24(h)(5), (i)(1), (i)(3). Index: C-CPI-U.

Rounding: next lowest multiple of $100 (the increase).

2026: 1,400 x I(2025)/I(2017) = 1,793.71, increase 393.71 rounded down to 300. Provenance rules ctc, ctc_8812.

• 26 U.S.C. 24 checked 2026-10-12
  The amount determined under subsection (d)(1)(A) with respect to any qualifying child shall not exceed $1,400; the $1,400 amount in subsection (h)(5) shall be increased by an amount equal to; determined by substituting "2017" for "2016" in subparagraph (A)(ii) thereof; if any increase under this subsection is not a multiple of $100, such increase shall be rounded to the next lowest multiple of $100
• Rev. Proc. 2025-32: 2026 inflation-adjusted items checked 2026-10-12
  the amount used in § 24(d)(1)(A) to determine the amount of the credit under § 24 that may be refundable is $1,700

fed-ctc-fixed: fixed in law

Child tax credit amounts fixed in law (§24(h)(3), (h)(4)(A), (h)(6)): 2026 other-dependent credit 500; phase-out threshold 400,000 joint / 200,000 others; refundable-credit earned income floor 2,500. No indexing provision.

Statute: §24(h)(3), (h)(4)(A), (h)(6).

§24(i) indexes only the $2,200 (rule fed-ctc) and the $1,400 refundable amount (rule fed-ctc-refundable). The $50 per $1,000 phase-out and the 15 percent refundable rate are rates. Provenance rule ctc_statute.

• 26 U.S.C. 24 checked 2026-10-12
  the threshold amount shall be $400,000 in the case of a joint return ($200,000 in any other case); shall be increased by $500 for each dependent of the taxpayer; Subsection (d)(1)(B)(i) shall be applied by substituting "$2,500" for "$3,000"

fed-ebl-threshold: indexed

The excess business loss threshold (§461(l)(3)(A)(ii)(II), (C)): 2026 256,000 / 512,000 joint. C-CPI-U, the §1(f)(3) cost-of-living adjustment with 2024 for 2016 (P.L. 119-21 §70601(b)), base $250,000 (200 percent joint), the amount rounded to the nearest $1,000.

Statute: §461(l)(3)(C). Index: C-CPI-U.

Rounding: "rounded to the nearest multiple of $1,000" (the amount).

Federal engine 2.3 (B2): read by POST /api/federal-tax's refusal of an excess business loss (the limit itself is not modelled).

• 26 U.S.C. 461 checked 2026-10-12
  $250,000 (200 percent of such amount in the case of a joint return); such amount shall be rounded to the nearest multiple of $1,000
• Rev. Proc. 2025-32 checked 2026-10-12
  $256,000 ($512,000 for joint returns)