Model D.C. TANF 60-month phase-down and hardship extensions

## Context

D.C. has adopted or proposed changes to TANF for households that have received benefits for 60 months or longer. Starting October 1, 2026, affected households face a reduction in benefits, and current DHS guidance says households may lose TANF entirely in FY28 and beyond unless they qualify for a hardship extension.

PolicyEngine-US currently models D.C. TANF cash assistance, but it does not model cumulative TANF receipt duration, hardship extensions, or the 60-month phase-down / termination rules. This likely overstates TANF for affected D.C. families in FY2027+.

## Current model behavior

- `dc_tanf` calculates the D.C. monthly benefit as `standard_payment - dc_tanf_countable_income`, capped at the standard payment.
- `dc_tanf_eligible` checks D.C. basic eligibility and work requirements.
- There is a generic `is_tanf_enrolled` input, but no variable for months of TANF receipt or whether a household qualifies for a hardship extension.
- A repo search did not find an existing `months_on_tanf`, `tanf_months`, `tanf_time_limit`, or similar variable.

Relevant files:

- `policyengine_us/variables/gov/states/dc/dhs/tanf/dc_tanf.py`
- `policyengine_us/variables/gov/states/dc/dhs/tanf/eligibility/dc_tanf_eligible.py`
- `policyengine_us/variables/gov/hhs/tanf/cash/eligibility/is_tanf_enrolled.py`
- `policyengine_us/parameters/gov/states/dc/dhs/tanf/standard_payment/amount.yaml`

## Sources

- D.C. DHS TANF Program Update, updated May 5, 2026: https://dhs.dc.gov/page/tanf-program-update
- D.C. Code § 4-205.11a, time limit for receipt of TANF benefits: https://code.dccouncil.gov/us/dc/council/code/sections/4-205.11a
- D.C. Code § 4-205.52, public assistance payment amounts and reduced local TANF amounts: https://code.dccouncil.gov/us/dc/council/code/sections/4-205.52
- D.C. Council FY2026 Committee on Human Services budget report discussing the 60-month policy: https://dccouncil.gov/wp-content/uploads/2025/06/FY2026-CHS-Budget-Recommendations-and-Report-Circulation-Draft.pdf

## Plausible implementation

This seems plausible to model mechanically, with a data caveat.

Suggested input variables:

- `tanf_months_received` or `tanf_months_on_assistance`: cumulative months of TANF receipt for the assistance unit/adult, monthly or year input.
- `dc_tanf_hardship_extension`: whether the D.C. household is exempted from the 60-month reduction/termination.

Suggested parameter structure:

- `parameters/gov/states/dc/dhs/tanf/time_limit/months.yaml`
- `parameters/gov/states/dc/dhs/tanf/time_limit/reduction.yaml` or similar, with FY-specific reduced payment-level factors.

Possible formula approach:

- Determine whether the assistance unit is over the 60-month threshold.
- If not over threshold, calculate D.C. TANF as current law does today.
- If over threshold and no hardship extension, apply the reduced D.C. payment-level factor for the relevant fiscal year before subtracting countable income, or zero benefits if the current source confirms full termination.
- If hardship extension applies, preserve the unreduced benefit.

## Open questions

- Confirm the exact current-law schedule. D.C. DHS guidance updated May 5, 2026 says FY28 and beyond benefits end for 60-month+ households unless hardship applies, while D.C. Code § 4-205.52 currently shows reduced local assistance amounts for FY2027-FY2030 and thereafter.
- Decide how to represent historical TANF receipt in household inputs and CPS/enhanced CPS data. If the microdata do not include cumulative TANF months, this may need to be an optional input with a default of 0 or a simulation assumption/imputation.
- Decide whether the 60-month rule should be generic TANF infrastructure or D.C.-specific first.

## Acceptance criteria

- D.C. TANF reflects the 60-month policy beginning October 1, 2026.
- Tests cover below-threshold, over-threshold without hardship, and over-threshold with hardship households.
- Tests cover the FY2027 reduction and FY2028+ treatment after confirming current law.
- Documentation or variable labels explain that `tanf_months_received` is a cumulative duration input, not annual benefit receipt.