MT joint elderlly 20Kpwages 10Kswages 5Kintrec 51Kgssi

[feenberg]

See http://taxsim.nber.org/out2psl/937

I believe TA correctly denies the property tax credit because household income exceeds $45,000. See: instructions for line 16 on pdf page 15 of:

https://taxsim.nber.org/historical_state_tax_forms/MT/2025/2025_Montana_Individual_Income_Tax_Return_Form_2_Instructions.pdf

PE allows $407 based on rentpaid of $17,139.

[PavelMakarchuk]

Per Mont. Code Ann. § 15-30-2337 + § 15-30-2338(1)(d): an individual "must have less than $45,000 of gross household income", where § 15-30-2337(4) defines gross household income as "all income received by all individuals of a household while they are members of the household," and § 15-30-2337(9)(a)(viii) explicitly includes "all payments received under federal social security except social security income paid directly to a nursing home".

For this filer:

• Wages: $30,000
• Interest: $5,280
• Social Security (all, not just taxable): $51,792
• Gross household income: ~$87,072 → far above the $45,000 cap → credit = $0

TAXSIM-35 and TaxAct correctly deny the credit. PE gives $407 due to two PE-US bugs:

1. mt_elderly_homeowner_or_renter_credit.py applies the multiplier p.multiplier.calc(gross_household_income) per person, but § 15-30-2337(4) defines GHI at the household level. Combined with PE-taxsim's 50/50 split of joint intrec/gssi inputs, each spouse's per-person GHI stays under $45K → full multiplier → $407 credit applied.
2. PE's gross_income_sources.yaml includes adjusted_gross_income_person, which only picks up the taxable SS portion (via tax_unit_taxable_social_security). § 15-30-2337(9)(a)(viii) requires ALL SS. With this filer's $51K of gross SS, only ~$20K is currently counted.

Fixing either (1) or (2) alone moves PE toward TAXSIM/TaxAct; fixing both is the legally-correct path. Filing a PE-US issue — does this read right to you?

[PavelMakarchuk]

Filed as PolicyEngine/policyengine-us#8547. Will close this once that PR lands.