Add dedicated South Carolina dependent exemption parameter

changelog.d/sc-dependent-exemption-parameter.added.md

@@ -0,0 +1 @@
+Added a dedicated South Carolina dependent exemption parameter (Section 12-6-1140), with the young child deduction (Section 12-6-1160) set equal to it; no change to calculated values.

policyengine_us/parameters/gov/states/sc/tax/income/deductions/dependent_exemption/amount.yaml

@@ -0,0 +1,34 @@
+description: South Carolina provides a dependent exemption of this amount per dependent. The young child deduction (Section 12-6-1160) is set equal to this amount.
+values:
+  2019-01-01: 4_100 # Value in the legal code, last updated in 2019.
+  2021-01-01: 4_300
+  2022-01-01: 4_430
+  2023-01-01: 4_610
+  2024-01-01: 4_790
+  2025-01-01: 4_930
+
+metadata:
+  unit: currency-USD
+  period: year
+  uprating: gov.irs.uprating
+  rounding:
+    type: downwards
+    interval: 10
+  label: South Carolina dependent exemption amount
+  reference:
+    # 12-6-1140(13) defines the dependent exemption amount; 12-6-1160 sets the
+    # young child deduction equal to it.
+    - title: SC Legal Code | SECTION 12-6-1140
+      href: https://www.scstatehouse.gov/code/t12c006.php
+    - title: SC Legal Code | SECTION 12-6-1160
+      href: https://www.scstatehouse.gov/code/t12c006.php
+    - title: SC 1040 tax form instructions (2025)
+      href: https://dor.sc.gov/sites/dor/files/forms/SC1040Instr_2025.pdf#page=16
+    - title: SC 1040 tax form instructions (2021)
+      href: https://dor.sc.gov/forms-site/Forms/IITPacket_2021.pdf#page=19
+    - title: SC 1040 tax form (2022)
+      href: https://dor.sc.gov/forms-site/Forms/SC1040_2022.pdf#page=2
+    - title: SC 1040 tax form instructions (2023)
+      href: https://dor.sc.gov/forms-site/Forms/IITPacket_2023.pdf#page=29
+    - title: SC 1040 tax form instructions (2024)
+      href: https://dor.sc.gov/forms-site/Forms/SC1040Instr_2024.pdf#page=16

policyengine_us/parameters/gov/states/sc/tax/income/deductions/young_child/amount.yaml

@@ -1,4 +1,4 @@
-description: South Carolina provides a young child deduction of this amount.
+description: South Carolina provides a young child deduction of this amount per dependent under age 6. Section 12-6-1160 sets it equal to the dependent exemption amount (Section 12-6-1140), but it is kept as its own parameter so the two can be modelled independently.
 values:
   2019-01-01: 4_100 # Value in the legal code, last updated in 2019.
   2021-01-01: 4_300
@@ -16,13 +16,13 @@ metadata:
     interval: 10
   label: South Carolina young child deduction amount
   reference:
+    # 12-6-1160 defines the young child deduction equal to the 12-6-1140 amount.
+    - title: SC Legal Code | SECTION 12-6-1160
+      href: https://www.scstatehouse.gov/code/t12c006.php
     - title: SC 1040 tax form instructions (2025)
       href: https://dor.sc.gov/sites/dor/files/forms/SC1040Instr_2025.pdf#page=16
     - title: SC 1040 tax form instructions (2021)
       href: https://dor.sc.gov/forms-site/Forms/IITPacket_2021.pdf#page=19
-    # 12-6-1160 defines the program and points to the amount in 1140.
-    - title: SC Legal Code | SECTION 12-6-1160
-      href: https://www.scstatehouse.gov/code/t12c006.php
     - title: SC 1040 tax form (2022)
       href: https://dor.sc.gov/forms-site/Forms/SC1040_2022.pdf#page=2
     - title: SC 1040 tax form instructions (2023)

policyengine_us/tests/policy/baseline/gov/states/sc/tax/income/exemptions/sc_dependent_exemption.yaml

@@ -6,10 +6,60 @@
   output:
     sc_dependent_exemption: 4_430
 
-- name: Case 2, family with 3 dependents, get 3 dependent exemptions. 
+- name: Case 2, family with 3 dependents, get 3 dependent exemptions.
   period: 2022
   input:
     state_code: SC
-    tax_unit_dependents: 3 
+    tax_unit_dependents: 3
   output:
     sc_dependent_exemption: 13_290
+
+# Case 3, repoint pin: prove sc_dependent_exemption reads the dedicated
+# dependent_exemption parameter, NOT the young_child parameter. Override both
+# to distinct values; the variable must reflect dependent_exemption and ignore
+# young_child. Without the repoint this case would fail.
+- name: Case 3, repoint pin - variable reads dependent_exemption, not young_child.
+  period: 2025
+  input:
+    state_code: SC
+    tax_unit_dependents: 2
+    # Distinct override values so the two parameters cannot be confused.
+    gov.states.sc.tax.income.deductions.dependent_exemption.amount: 9_000
+    gov.states.sc.tax.income.deductions.young_child.amount: 1_000
+  output:
+    # 2 dependents * $9,000 (dependent_exemption) = $18,000.
+    # If the variable still read young_child it would be 2 * $1,000 = $2,000.
+    sc_dependent_exemption: 18_000
+
+# Case 4, stacking: an under-6 dependent qualifies for BOTH the dependent
+# exemption (12-6-1140) and the young child deduction (12-6-1160). They are
+# separate provisions and must stack - check each independently.
+- name: Case 4, under-6 dependent stacks dependent exemption and young child deduction.
+  period: 2025
+  input:
+    people:
+      person1: {}
+      person2:
+        age: 5
+    tax_units:
+      tax_unit:
+        members: [person1, person2]
+    households:
+      household:
+        members: [person1, person2]
+        state_code: SC
+  output:
+    # 2025 amount is $4,930; 1 dependent.
+    sc_dependent_exemption: 4_930
+    # Same child is under 6, so the young child deduction also applies.
+    sc_young_child_deduction: 4_930
+
+# Case 5, per-year symmetry: 2025 dependent exemption at the baseline amount.
+- name: Case 5, 3 dependents in 2025 get 3 dependent exemptions.
+  period: 2025
+  input:
+    state_code: SC
+    tax_unit_dependents: 3
+  output:
+    # 2025 dependent exemption amount is $4,930; 3 * $4,930 = $14,790.
+    sc_dependent_exemption: 14_790

policyengine_us/variables/gov/states/sc/tax/income/exemptions/sc_dependent_exemption.py

@@ -15,8 +15,8 @@ class sc_dependent_exemption(Variable):
     defined_for = StateCode.SC
 
     def formula(tax_unit, period, parameters):
-        # Get relevant parameter subtree. The amount for dependent exemption is the same amount as the the young_child's.
-        p = parameters(period).gov.states.sc.tax.income.deductions.young_child
+        # Section 12-6-1140(13): a dependent exemption for every dependent.
+        p = parameters(period).gov.states.sc.tax.income.deductions.dependent_exemption
         # every dependent is eligible
         dependents = tax_unit("tax_unit_dependents", period)
         # Multiply by the amount per exemption.