Give the Illinois 2021 income tax rebate base amount at negative AGI

changelog.d/il-rebate-negative-agi.fixed.md

@@ -0,0 +1 @@
+Give the Illinois 2021 income tax rebate base amount to filers with negative federal AGI.

policyengine_us/tests/policy/baseline/gov/states/il/tax/income/credits/il_income_tax_rebate.yaml

@@ -47,3 +47,33 @@
     tax_unit_dependents: 0
   output:
     il_income_tax_rebate: 50
+
+- name: Single with negative AGI gets the base rebate
+  period: 2021
+  input:
+    adjusted_gross_income: -2_000
+    filing_status: SINGLE
+    state_code: IL
+    tax_unit_dependents: 0
+  output:
+    il_income_tax_rebate: 50
+
+- name: Single with negative AGI and one dependent
+  period: 2021
+  input:
+    adjusted_gross_income: -2_000
+    filing_status: SINGLE
+    state_code: IL
+    tax_unit_dependents: 1
+  output:
+    il_income_tax_rebate: 150
+
+- name: Joint with negative AGI and two dependents
+  period: 2021
+  input:
+    adjusted_gross_income: -500_000
+    tax_unit_is_joint: true
+    state_code: IL
+    tax_unit_dependents: 2
+  output:
+    il_income_tax_rebate: 300

policyengine_us/variables/gov/states/il/tax/income/credits/il_income_tax_rebate.py

@@ -13,11 +13,14 @@ class il_income_tax_rebate(Variable):
     def formula(tax_unit, period, parameters):
         p = parameters(period).gov.states.il.tax.income.credits.income_tax_rebate
         federal_agi = tax_unit("adjusted_gross_income", period)
+        # Section 212.1(a) sets only an upper AGI limit, so a negative AGI
+        # receives the full base amount; the scales start at zero.
+        scale_agi = max_(federal_agi, 0)
         joint = tax_unit("tax_unit_is_joint", period)
         base_amount = where(
             joint,
-            p.amount.joint.calc(federal_agi),
-            p.amount.other.calc(federal_agi),
+            p.amount.joint.calc(scale_agi),
+            p.amount.other.calc(scale_agi),
         )
         dependent_count = tax_unit("tax_unit_dependents", period)
         capped_dependents = min_(dependent_count, p.max_dependents)