Book Connecticut child tax rebate in 2021 eligibility year (like RI/NM)

[DTrim99]

Fixes #9270. Surfaced by PolicyEngine/policyengine-taxsim#1127.

Problem

The Connecticut 2022 Child Tax Rebate (PA 22-118) is $250/child (max 3), determined by the 2021 return, claimed by a separate application (June–July 2022), and paid in fall 2022 — CT DRS overview. It is not a line on the CT-1040.

PolicyEngine listed ct_child_tax_rebate among Connecticut's 2022 non-refundable income-tax credits, so it reduced 2022 CT income tax (e.g. a HoH with one child and CT AGI $54,934: CT income tax 2,094 → 1,844) and computed eligibility from 2022 income/dependents. TaxAct's 2022 CT-1040 shows CT income tax $2,094 with no rebate.

PolicyEngine already books the directly analogous prior-year rebates in the eligibility year: ri_child_tax_rebate (RI's $250/child, 2021-return-based, paid Oct 2022) and nm_2021_income_rebate are both in their 2021 refundable lists. Connecticut's was the outlier.

Fix

Mirror ri_child_tax_rebate:

• Remove ct_child_tax_rebate from ct/tax/income/credits/non_refundable.yaml (2022).
• Add it to ct/tax/income/credits/refundable.yaml under 2021-01-01 (removed 2022) — refundable, since the rebate is a check paid regardless of tax liability.
• Shift the rebate parameters (amount, child_cap, reduction/*) from 2022-01-01 to 2021-01-01, so eligibility is computed from 2021 income/dependents.
• Move the ct_child_tax_rebate unit tests to period 2021 (amounts unchanged).
• Zero ct_child_tax_rebate in the two 2021 CT integration tests (their expected ct_income_tax comes from TAXSIM35, which does not model the rebate) — following the existing ri_child_tax_rebate: 0 convention in the RI integration test.

Result

2022 CT income tax no longer includes the rebate ($2,094, matching the CT-1040), and Connecticut is consistent with the eligibility-year treatment PolicyEngine uses for Rhode Island and New Mexico. Full CT baseline suite passes.

[PavelMakarchuk]

The re-booking mechanics themselves check out — parameter start dates, the refundable/non-refundable list moves, the RI/NM analog pattern, no impact on the CT contrib reforms, and the full CT tax suite (136 tests) plus the cross-state income tax suite (67 tests) pass on this branch.

Requesting changes for four findings, detailed inline:

1. Phase-out uses ct_agi instead of federal AGI (ct_child_tax_rebate.py:13) — PA 22-118 phased out on federal AGI from the 2021 return. Pre-existing line, but this PR is what books the formula into the live 2021 baseline.
2. Counts all dependents, not children 18 or younger (ct_child_tax_rebate.py:25) — the program required a dependent child age 18 or younger; cf. ri_child_tax_rebate's age check.
3. No 2022 sunset on the rebate parameters — ct_child_tax_rebate returns $250/child for 2023+ when queried directly.
4. Stale test name — "Head of household with $170,000 AGI" vs. ct_agi: 165_000 input.

Findings 1 and 2 are the substantive ones: they change real 2021 microsim outputs, and the current unit tests mask both by injecting ct_agi and tax_unit_count_dependents directly.

Sources: CT DRS Child Tax Rebate overview, CT OLR 2026-R-0020

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[DTrim99]

Fixes applied from @PavelMakarchuk's review

All four findings addressed and pushed (CT tax suite 140/140). Thanks — the substantive two were both masked by the injected-input tests, exactly as you noted.

F1 — phase-out on federal AGI (fixed)

Switched the phase-out income measure in ct_child_tax_rebate.py from ct_agi to adjusted_gross_income, matching PA 22-118 (federal AGI from the 2021 return). Your case — federal AGI $110k with CT subtractions dropping ct_agi to $95k — now correctly triggers the reduction instead of paying the full rebate.

F2 — count only dependent children ≤18 (fixed)

Replaced tax_unit_count_dependents with the RI-style age gate: (age <= p.age_limit) & is_tax_unit_dependent, summed over members and capped. Added a ct/tax/income/rebate/age_limit parameter (18, referenced to CT DRS / OLR 2026-R-0020 / PA 22-118 §410). A unit whose only dependent is 21 now gets 0; mixed minor+adult units count only the minors.

F3 — 2022 sunset (fixed)

Added 2022-01-01: 0 to amount.yaml and child_cap.yaml (with a note that the credit was a one-time 2021 payment), so the variable is inert for 2022+ and can't be silently resurrected. I did not zero the reduction.increment (it's a divisor — that would introduce a div-by-zero); zeroing amount and cap fully sunsets the rebate.

F4 + test coverage

• Fixed the stale name: the case is now "$165,000 federal AGI" to match its input (expected 250).
• Since F1/F2 changed which inputs the formula reads, rewrote the 3 existing cases to inject adjusted_gross_income and real dependents with ages instead of ct_agi/tax_unit_count_dependents.
• Added cases that each fail if the corresponding fix is reverted: age-21-only dependent → 0; mixed minor+adult → 250; federal AGI $130k with ct_agi $90k → 0 (federal phase-out); 2023 unit with a child → 0 (sunset).

No 2021 parameter values changed.

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