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Montana's taxsim_state_agi is 0 from 2024 and unpooled on 2021–2023 joint returns #9929
Description
What is wrong
gov.states.household.state_agis lists mt_agi_indiv as Montana's state AGI. taxsim_state_agi (and its deprecated alias state_agi) adds that list over the tax unit. This causes two errors:
- From 2024 Montana's state AGI is 0.
mt_agi_indivisdefined_for = "mt_married_filing_separately_on_same_return_eligible", which is false from 2024 (Montana repealed filing separately on the same form; commit 2a20d65). - 2021–2023 joint returns are not pooled.
mt_agi_indivfloors each spouse's Montana AGI at zero before the sum. A joint return's Montana AGI (Form 2 page 1, line 14, one column) pools the spouses first. That figure ismt_agi_joint.
Household runs on main (b79705b), state MT:
| Year | Household | mt_agi_joint |
taxsim_state_agi |
|---|---|---|---|
| 2022 | single, wages 100,000 | 100,000 | 100,000 |
| 2022 | couple: head wages 100,000; spouse Schedule C −20,000 | 80,000 | 90,000 |
| 2024 | single, wages 100,000 | 100,000 | 0 |
| 2026 | single, wages 100,000 | 100,000 | 0 |
taxsim_state_agi feeds TAXSIM comparisons. The only in-repo consumer is policyengine_us/tests/policy/baseline/gov/tax/income/test_legacy_state_umbrellas.py. Montana's income tax itself is unaffected, because it uses mt_agi_joint and the _indiv path directly.
Fix
Report the return's Montana AGI for the filing path actually used. Use mt_agi_joint on the joint path and the sum of mt_agi_indiv when mt_files_separately; a generated mt_agi like mt_taxable_income's _generate_state_mfs_variables entry would do. Then list that variable in state_agis.yaml. From 2024 Montana has no AGI line: Form 2 starts from federal taxable income. Decide whether TAXSIM's state-AGI column should then carry federal AGI or PE's mt_agi_joint intermediate, and document the choice.
Found while working on #9903.
Activity
Report Montana's TAXSIM state AGI for the filing path used, and feder…