Add Colorado alternative minimum tax

changelog_entry.yaml

@@ -0,0 +1,4 @@
+- bump: minor
+  changes:
+    added:
+      - Colorado alternative minimum tax (AMT).

policyengine_us/parameters/gov/states/co/tax/income/amt/rate.yaml

@@ -0,0 +1,13 @@
+description: Colorado alternative minimum tax rate
+values:
+  2021-01-01: 0.0347
+
+metadata:
+  label: Colorado AMT rate
+  period: year
+  unit: /1
+  reference:
+    - title: Colorado DR 0104AMT Instructions
+      href: https://tax.colorado.gov/DR0104AMT
+    - title: C.R.S. § 39-22-105
+      href: https://law.justia.com/codes/colorado/2022/title-39/article-22/part-1/section-39-22-105/

policyengine_us/tests/policy/baseline/gov/states/co/tax/income/amt/co_alternative_minimum_taxable_income.yaml

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+# Colorado alternative minimum taxable income tests
+- name: CO AMTI calculation
+  period: 2024
+  input:
+    amt_income_less_exemptions: 200_000
+    co_additions: 10_000
+    co_subtractions: 5_000
+    state_code: CO
+  output:
+    # 200,000 + 10,000 - 5,000 = 205,000
+    co_alternative_minimum_taxable_income: 205_000
+
+- name: CO AMTI with no federal AMT income
+  period: 2024
+  input:
+    amt_income_less_exemptions: 0
+    co_additions: 10_000
+    co_subtractions: 5_000
+    state_code: CO
+  output:
+    # 0 + 10,000 - 5,000 = 5,000
+    co_alternative_minimum_taxable_income: 5_000
+
+- name: CO AMTI cannot be negative
+  period: 2024
+  input:
+    amt_income_less_exemptions: 0
+    co_additions: 0
+    co_subtractions: 50_000
+    state_code: CO
+  output:
+    # max(0, 0 + 0 - 50,000) = 0
+    co_alternative_minimum_taxable_income: 0

policyengine_us/tests/policy/baseline/gov/states/co/tax/income/amt/co_amt.yaml

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+# Colorado Alternative Minimum Tax tests
+- name: No AMT when normal tax exceeds tentative minimum tax
+  period: 2024
+  input:
+    co_tentative_minimum_tax: 5_000
+    co_income_tax_before_non_refundable_credits: 10_000
+    state_code: CO
+  output:
+    co_amt: 0
+
+- name: AMT when tentative minimum tax exceeds normal tax
+  period: 2024
+  input:
+    co_tentative_minimum_tax: 15_000
+    co_income_tax_before_non_refundable_credits: 10_000
+    state_code: CO
+  output:
+    co_amt: 5_000

policyengine_us/tests/policy/baseline/gov/states/co/tax/income/amt/co_tentative_minimum_tax.yaml

@@ -0,0 +1,9 @@
+# Colorado tentative minimum tax tests
+- name: Tentative minimum tax calculation
+  period: 2024
+  input:
+    co_alternative_minimum_taxable_income: 100_000
+    state_code: CO
+  output:
+    # 100,000 * 0.0347 = 3,470
+    co_tentative_minimum_tax: 3_470

policyengine_us/variables/gov/states/co/tax/income/amt/co_alternative_minimum_taxable_income.py

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+from policyengine_us.model_api import *
+
+
+class co_alternative_minimum_taxable_income(Variable):
+    value_type = float
+    entity = TaxUnit
+    label = "Colorado alternative minimum taxable income"
+    unit = USD
+    definition_period = YEAR
+    defined_for = StateCode.CO
+    reference = [
+        "https://tax.colorado.gov/DR0104AMT",
+        "https://law.justia.com/codes/colorado/2022/title-39/article-22/part-1/section-39-22-105/",
+    ]
+
+    def formula(tax_unit, period, parameters):
+        # DR 0104AMT calculation:
+        # Line 1: Federal Form 6251 line 6 (federal AMTI less exemption)
+        federal_amt_income_less_exemptions = tax_unit(
+            "amt_income_less_exemptions", period
+        )
+        # Line 2: Colorado additions (from DR 0104, lines 3-8)
+        co_additions = tax_unit("co_additions", period)
+        # Line 4: Colorado subtractions (excluding state income tax refund)
+        co_subtractions = tax_unit("co_subtractions", period)
+        # Line 5: Colorado AMTI
+        return max_(
+            0,
+            federal_amt_income_less_exemptions
+            + co_additions
+            - co_subtractions,
+        )

policyengine_us/variables/gov/states/co/tax/income/amt/co_amt.py

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+from policyengine_us.model_api import *
+
+
+class co_amt(Variable):
+    value_type = float
+    entity = TaxUnit
+    label = "Colorado alternative minimum tax"
+    unit = USD
+    definition_period = YEAR
+    defined_for = StateCode.CO
+    reference = [
+        "https://tax.colorado.gov/DR0104AMT",
+        "https://law.justia.com/codes/colorado/2022/title-39/article-22/part-1/section-39-22-105/",
+    ]
+
+    def formula(tax_unit, period, parameters):
+        tentative_minimum_tax = tax_unit("co_tentative_minimum_tax", period)
+        # Normal tax before non-refundable credits
+        normal_tax = tax_unit(
+            "co_income_tax_before_non_refundable_credits", period
+        )
+        # AMT is the excess of tentative minimum tax over normal tax
+        return max_(0, tentative_minimum_tax - normal_tax)

policyengine_us/variables/gov/states/co/tax/income/amt/co_tentative_minimum_tax.py

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+from policyengine_us.model_api import *
+
+
+class co_tentative_minimum_tax(Variable):
+    value_type = float
+    entity = TaxUnit
+    label = "Colorado tentative minimum tax"
+    unit = USD
+    definition_period = YEAR
+    defined_for = StateCode.CO
+    reference = [
+        "https://tax.colorado.gov/DR0104AMT",
+        "https://law.justia.com/codes/colorado/2022/title-39/article-22/part-1/section-39-22-105/",
+    ]
+
+    def formula(tax_unit, period, parameters):
+        co_amti = tax_unit("co_alternative_minimum_taxable_income", period)
+        p = parameters(period).gov.states.co.tax.income.amt
+        # DR 0104AMT Line 6: multiply by 3.47%
+        return co_amti * p.rate

policyengine_us/variables/gov/states/co/tax/income/co_income_tax.py

@@ -9,5 +9,5 @@ class co_income_tax(Variable):
     definition_period = YEAR
     defined_for = StateCode.CO
 
-    adds = ["co_income_tax_before_refundable_credits"]
+    adds = ["co_income_tax_before_refundable_credits", "co_amt"]
     subtracts = ["co_refundable_credits"]