Model Medicare Part B premiums net of MSP coverage

[MaxGhenis]

Summary

• Models Medicare Part B premiums as beneficiary out-of-pocket premiums net of Medicare Savings Program coverage.
• Adds gross_medicare_part_b_premium for the pre-MSP premium used by Medicare cost/value calculations.
• Keeps reported Part B premiums as a separate audit input and removes the legacy plural Part B premium formula path after the clean MOOP decomposition.
• Nets out a cycle-free MSP proxy so likely MSP-covered standard premiums do not count toward baseline SPM MOOP, while IRMAA above the standard premium remains out of pocket.

Testing

• uv run pytest -q policyengine_us/tests/policy/baseline/gov/hhs/medicare/test_part_b_msp_offset.py
• uv run python -m policyengine_core.scripts.policyengine_command test policyengine_us/tests/policy/baseline/gov/hhs/medicare/costs/medicare_cost.yaml policyengine_us/tests/policy/baseline/gov/hhs/medicare/eligibility/medicare_part_b_premium.yaml policyengine_us/tests/policy/baseline/gov/hhs/medicare/savings_programs/msp_part_b_premium_coverage.yaml policyengine_us/tests/policy/baseline/household/income/spm_unit/spm_unit_medical_out_of_pocket_expenses.yaml policyengine_us/tests/policy/baseline/household/income/spm_unit/spm_unit_medical_out_of_pocket_expenses_medicare_part_b.yaml policyengine_us/tests/policy/baseline/gov/states/nj/tax/income/exclusions/nj_other_retirement_income_exclusion.yaml policyengine_us/tests/policy/baseline/gov/states/nj/tax/income/integration.yaml policyengine_us/tests/policy/baseline/gov/states/nj/tax/income/subtractions/nj_social_security_exclusion.yaml policyengine_us/tests/policy/baseline/gov/states/nm/tax/income/integration.yaml policyengine_us/tests/policy/baseline/gov/states/oh/tax/income/integration.yaml -c policyengine_us
• uv run ruff check policyengine_us/variables/gov/hhs/medicare/eligibility/part_b/gross_medicare_part_b_premium.py policyengine_us/variables/gov/hhs/medicare/eligibility/part_b/medicare_part_b_premium.py policyengine_us/variables/gov/hhs/medicare/costs/medicare_cost.py policyengine_us/tests/policy/baseline/gov/hhs/medicare/test_part_b_msp_offset.py
• git diff --check

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (d888043) to head (188d7b1).
⚠️ Report is 19 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##             main     #7972       +/-   ##
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+ Coverage   86.04%   100.00%   +13.95%     
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  Files           3         7        +4     
  Lines          43       104       +61     
  Branches        2         1        -1     
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+ Hits           37       104       +67     
+ Misses          6         0        -6     

Flag	Coverage Δ
unittests	100.00% <100.00%> (+13.95%)	⬆️

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[daphnehanse11]

I found one P1 policy issue in the MSP asset-test parameterization. Details and sources are inline.

[daphnehanse11]

MA and ME should not apply the MSP asset test here. Maine's MSP statute says DHHS may not apply an asset test when determining MSP eligibility, and Massachusetts eliminated MSP resource tests for these programs in 2024. With the current true entries, I reproduced a 2025 low-income Medicare enrollee in both MA and ME with $20k in bank assets returning msp_asset_eligible = false, msp_part_b_premium_coverage = 0, and medicare_part_b_premium = 2,220, which overstates SPM MOOP by the standard Part B premium. Please set ME and MA to false from the applicable effective dates and add regression coverage.

Sources:

• Maine Title 22, §3174-LLL
• Massachusetts FY2024 budget summary, Medicare Savings Program Asset Test Elimination
• Mass.gov, Medicare Savings Program information