Minnesota working family credit: filers 65+ whose only qualifying child is 18 or older get $0 #9951

Summary

mn_wfc_eligible decides whether a filer with children can get the Minnesota working family credit by tax_unit_children > 0, which counts only people under 18. A filer whose only qualifying children are 18 or older (a student aged 19-23, a disabled adult child, or, with #9922, an 18-year-old) is then treated as childless, and the childless-adult age range (25-64) applies. A filer aged 65 or older with such a child gets $0, although the federal EITC pays.

Repro (main, 2025)

from policyengine_us import Simulation
def run(head_age):
    s = Simulation(situation={"people": {
        "h": {"age": {2025: head_age}, "employment_income": {2025: 10_000}},
        "k": {"age": {2025: 20}, "is_tax_unit_dependent": {2025: True}, "is_full_time_student": {2025: True}}},
        "tax_units": {"t": {"members": ["h", "k"]}},
        "households": {"hh": {"members": ["h", "k"], "state_code": {2025: "MN"}}}})
    return s.calculate("eitc", 2025)[0], s.calculate("mn_child_and_working_families_credits", 2025)[0], s.calculate("mn_wfc_eligible", 2025)[0]
print(run(40))  # (3400.0, 1379.2, True)
print(run(66))  # (3400.0, 0.0, False)

The 66-year-old has a federal EITC qualifying child (a 20-year-old full-time student) and gets the $3,400 federal EITC, but $0 Minnesota credit. The statute gives $379.20 + $1,000 (qualifying older child) = $1,379.20, as for the 40-year-old.

Law

Minn. Stat. 290.0671, subd. 1(a) allows the working family credit to an individual "who is eligible for the credit under section 32 of the Internal Revenue Code" (with the Minnesota modifications in subd. 1a). Under 26 U.S.C. 32(c)(1)(A), the age range applies only to an eligible individual who does not have a qualifying child; with a qualifying child (any 32(c) qualifying child, including students under 24 and disabled children of any age) there is no filer age limit.

Expected fix

Test for a 32(c) qualifying child in mn_wfc_eligible (for example is_qualifying_child_dependent / is_eitc_qualifying_child, as #9643 uses in the credit formula), not tax_unit_children.

Found while reviewing #9922.