[MaxGhenis]

Summary

backdate_parameters (policyengine_us/tools/parameters.py) copies each parameter's earliest value back to 2015 (FIRST_MODELED_YEAR). Hawaii parameters first dated after 2015 therefore applied in years before the law existed. This PR dates them. It changes no formula, and the 2018–2022 nonrefundable EITC is unchanged.

	Before (single, age 30, $8,000 wages)	After
Act 115 refund in hi_refundable_credits	$300 in 2021 only (main's #10309 already zeroes the amounts before 2021)	unchanged; the 2015–2020 list now omits it too
hi_eitc_potential	20% of the federal EITC from 2015	0 before 2018; 20% for 2018–2022; 40% from 2023
hi_income_tax 2017	−$396.21	$5.79
hi_military_pay_exclusion cap	$7,345 for 2015–2022; $8,315 (uprated) for 2025	each year's N-11 amount

Changes

• credits/refundable.yaml: a 2000-01-01 block without hi_act_115_rebate. Act 115 (SLH 2022) refunds went only to filers of a 2021 Form N-11 (DOTAX Announcement 2022-03, p.2). The 2018 Form N-11 lists the same three modeled refundable credits (p.3).
• credits/act_115_rebate/{single,joint}.yaml: no change. This PR first dated the amounts to 2021 only. Main's Guard historical state rebate eligibility and document attribution #10309 has since dated them 2020-01-01: 0, which zeroes 2015–2020, and keeps the 2022+ schedules on purpose for standalone calculations. The merge takes main's files, so the dated refundable list keeps the refund out of 2022 and later. The 2022 tests now check hi_refundable_credits rather than the standalone refund.
• credits/non_refundable.yaml: 2000-01-01: [], 2018-01-01: [hi_eitc], 2023-01-01: [].
• credits/eitc/match.yaml: 2000-01-01: 0, 2018-01-01: 0.2 (was 2017-01-01: 0.2). The credit is "effective for taxable years beginning after December 31, 2017" (2018 Form N-356, p.2; Act 107, SLH 2017, per 2018 N-11 instructions, p.2). gov/states/household/state_eitcs.yaml already starts hi_eitc in 2018.
• subtractions/military_pay/cap.yaml: the file held the 2022 amount ($7,345) from 2021, so 2015–2021 used it. It now has each year's N-11 instructions line 15 amount: 2015 $6,198, 2016 $6,279, 2017 $6,410, 2018 $6,564, 2019 $6,735, 2020 $6,943, 2021 $7,152, 2022 $7,345, 2023 $7,683, 2024 $8,082, 2025 $8,636. 2026 onward is still projected by gov.irs.uprating, now from $8,636. The 2015–2017 instructions are cited from the Wayback Machine because DOTAX removed them.

Audit of the other Hawaii income tax parameters first dated after 2015

I checked each against the 2015–2022 N-11 instructions, Form N-311 (2016–2022) and Schedule X (2015, 2017–2021, 2023):

Parameter (first date)	Result
Food/excise credit amounts, minor-child $110, age and support thresholds (2021)	Match 2016–2022. 2015 differs: Act 223 (SLH 2015) raised the amounts from 2016, and the 2015 minor-child amount was $85 (2015 Schedule X line 9). Listed as a follow-up.
Renters' credit $50, AGI under $30,000, rent over $1,000, age 65 (2021)	Match 2015–2023
Exemption $1,144, disability exemption $7,000, aged threshold 65 (2021)	Match 2015–2022
Itemized deduction limitation threshold $166,800 / $83,400 (2021)	Match 2015–2022
Alternative tax on capital gains, 7.25% (2021)	Match 2015–2022
Standard deduction $2,200 / $4,400 / $3,212 (2022)	Match 2015–2021
Rates (2018)	2016–2017 differ: Act 107 (SLH 2017) reinstated the top three brackets from 2018 (2017 N-11 instructions p.2); 2015 had them under Act 60 (SLH 2009). Out of this PR's scope; listed as a follow-up.
CDCC rate table (2018)	Matches the 2017 Schedule X

Not audited: the composition of subtractions/subtractions.yaml.

Tests

• YAML: credits/hi_credit_start_dates.yaml (2016, 2017, 2018, 2020, 2021, 2022) and new cases in hi_eitc.yaml, hi_act_115_rebate.yaml and hi_military_pay_exclusion.yaml. The existing 2021 military cap case now expects $7,152. On main, 16 of these cases fail, all in the years the model was wrong; the 2018, 2020 and 2021 EITC cases and the 2021 refund cases pass on both and guard the years that were right.
• tests/unit/test_hi_credit_start_dates_properties.py: a 108-household grid and Hypothesis-generated batches in every year 2015–2026, plus a differential test of the exclusion against each year's published cap. On main, 15 of the 17 tests fail.
• All 535 cases in the Hawaii baseline and contrib YAML tests and household_state_income_tax.yaml pass, as do salt_refund_integration.yaml and the contrib federal abolition test.
• In a trial merge with Model Hawaii's claim of right deduction and credit (section 1341 as operative in Hawaii from 2022) #10200 and Apply Hawaii refundable credits before nonrefundable credits #10202, all 543 Hawaii YAML cases, these property tests and test_hi_credit_ordering.py pass. The new cases avoid asserting hi_income_tax in 2018–2022, where Apply Hawaii refundable credits before nonrefundable credits #10202 changes the credit order.

Invariants (checked for every grid point and generated household, 2015–2026)

• hi_act_115_rebate is 0 before 2021. In 2021 it is $300, or $100 at or above $100,000 federal AGI ($200,000 for joint filers and surviving spouses), times the number of people on the return. It enters hi_refundable_credits only in 2021.
• hi_eitc_potential equals the year's match rate (0 before 2018, 0.2 for 2018–2022, 0.4 from 2023) times eitc.
• hi_non_refundable_credits is 0 before 2018 and from 2023. In 2018–2022 it lies between 0 and min(hi_eitc_potential, tax before nonrefundable credits).
• hi_refundable_credits minus the food/excise, dependent care and renters' credits equals the Act 115 refund in 2021, hi_eitc from 2023, and 0 otherwise.
• Before 2018, hi_income_tax equals tax before credits minus refundable credits.
• hi_military_pay_exclusion equals min(pay, the year's published cap) for 2015–2025 (differential against the instructions).

Merge with main (2026-11-03)

• act_115_rebate/{single,joint}.yaml and hi_act_115_rebate.yaml conflicted with Guard historical state rebate eligibility and document attribution #10309. The merge takes main's amount files and keeps both sides' test cases. "No refund for 2022" became "No refund in 2022 refundable credits".
• hi_credit_start_dates.yaml case 5 and the property test now check the 2022+ refund through hi_refundable_credits.
• Apply Hawaii refundable credits before nonrefundable credits #10202 is on main. test_hi_credit_ordering.py passes on the merged head.

Sources

The adopting session on 2026-11-03 could not refetch the DOTAX, Wayback or HRS sources: its network policy blocked files.hawaii.gov, web.archive.org and capitol.hawaii.gov. The military pay caps and the Act 107 date are as an earlier session recorded them. A reviewer with web access should confirm them.

Axiom note

Axiom's Hawaii income tax modules cover tax year 2026 only, and this PR changes 2015–2025 values.

impact: the hub will measure
axiom: (hub files pe-parity before landing)

Coordination: #10202 has merged. #10200 adds hi_claim_of_right_credit to the 2022+ blocks of refundable.yaml and merges cleanly with this PR.

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Generated by Claude Code

[MaxGhenis]

Picking this up for the US hub. I'll post a hand-off comment here when it's ready.

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Generated by Claude Code

[MaxGhenis]

Picking this up for the US hub. I continue an earlier session's work: it picked this PR up on 2026-11-02 and stopped before pushing anything. I'll post a hand-off comment here when it's ready.

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Generated by Claude Code

[MaxGhenis]

Picking this up for the US hub. I continue the earlier sessions' work on this PR; they pushed nothing. I'll post a hand-off comment here when it's ready.

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Generated by Claude Code