Add Montana newborn credit reform

changelog.d/mt-newborn-credit.added.md

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+Add Montana newborn credit reform.

policyengine_us/parameters/gov/contrib/states/mt/newborn_credit/age_limit.yaml

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+description: Montana limits child age to this threshold under the newborn credit program.
+
+values:
+  2027-01-01: 1
+
+metadata:
+  unit: year
+  period: year
+  label: Montana newborn credit child age limit

policyengine_us/parameters/gov/contrib/states/mt/newborn_credit/amount.yaml

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+description: Montana provides this amount per qualifying child under the newborn credit program.
+
+values:
+  2027-01-01: 1_000
+
+metadata:
+  unit: currency-USD
+  period: year
+  label: Montana newborn credit amount

policyengine_us/parameters/gov/contrib/states/mt/newborn_credit/in_effect.yaml

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+description: Montana uses this indicator to determine whether the newborn credit reform is in effect.
+
+values:
+  0000-01-01: false
+
+metadata:
+  unit: bool
+  period: year
+  label: Montana newborn credit in effect

policyengine_us/parameters/gov/contrib/states/mt/newborn_credit/reduction/amount.yaml

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+description: Montana sets this amount as the phase-out reduction per income increment under the newborn credit program.
+
+values:
+  2027-01-01: 50
+
+metadata:
+  unit: currency-USD
+  period: year
+  label: Montana newborn credit reduction amount

policyengine_us/parameters/gov/contrib/states/mt/newborn_credit/reduction/increment.yaml

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+description: Montana sets this amount as the income increment for phase-out calculations under the newborn credit program.
+
+values:
+  2027-01-01: 1_000
+
+metadata:
+  unit: currency-USD
+  period: year
+  label: Montana newborn credit reduction increment

policyengine_us/parameters/gov/contrib/states/mt/newborn_credit/reduction/threshold.yaml

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+description: Montana limits the newborn credit to taxpayers with AGI at or below this amount.
+
+SINGLE:
+  values:
+    2027-01-01: 60_000
+
+HEAD_OF_HOUSEHOLD:
+  values:
+    2027-01-01: 60_000
+
+JOINT:
+  values:
+    2027-01-01: 120_000
+
+SEPARATE:
+  values:
+    2027-01-01: 60_000
+
+SURVIVING_SPOUSE:
+  values:
+    2027-01-01: 120_000
+
+metadata:
+  unit: currency-USD
+  period: year
+  label: Montana newborn credit phase-out threshold
+  breakdown:
+    - filing_status

policyengine_us/reforms/reforms.py

@@ -88,6 +88,9 @@
 from .states.mt.ctc import (
     create_mt_ctc_reform,
 )
+from .states.mt.newborn_credit import (
+    create_mt_newborn_credit_reform,
+)
 from .congress.golden import (
     create_fisc_act_reform,
 )
@@ -281,6 +284,7 @@ def create_structural_reforms_from_parameters(parameters, period):
         create_nyc_school_tax_credit_with_phase_out_reform(parameters, period)
     )
     mt_ctc = create_mt_ctc_reform(parameters, period)
+    mt_newborn_credit = create_mt_newborn_credit_reform(parameters, period)
     fisc_act = create_fisc_act_reform(parameters, period)
     tax_employer_social_security_tax = (
         create_tax_employer_social_security_tax_reform(parameters, period)
@@ -409,6 +413,7 @@ def create_structural_reforms_from_parameters(parameters, period):
         limit_salt_deduction_to_property_taxes,
         nyc_school_tax_credit_with_phase_out,
         mt_ctc,
+        mt_newborn_credit,
         fisc_act,
         tax_employer_social_security_tax,
         tax_employer_medicare_tax,

policyengine_us/reforms/states/mt/newborn_credit/__init__.py

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+from .mt_newborn_credit import create_mt_newborn_credit_reform

policyengine_us/reforms/states/mt/newborn_credit/mt_newborn_credit.py

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+from policyengine_us.model_api import *
+from policyengine_core.periods import period as period_
+from policyengine_core.periods import instant
+
+
+def create_mt_newborn_credit() -> Reform:
+    """Montana newborn credit reform.
+
+    Provides a $1,000 refundable credit per qualifying child under
+    age 1 with phase-out based on AGI. This is a PolicyEngine-designed
+    contrib reform; no enacted legislation exists.
+    """
+
+    class mt_newborn_credit_eligible_child(Variable):
+        value_type = bool
+        entity = Person
+        label = "Montana newborn credit eligible child"
+        definition_period = YEAR
+        defined_for = StateCode.MT
+
+        def formula(person, period, parameters):
+            p = parameters(period).gov.contrib.states.mt.newborn_credit
+            age = person("age", period)
+            is_dependent = person("is_tax_unit_dependent", period)
+            has_ssn = person("meets_eitc_identification_requirements", period)
+            return (age < p.age_limit) & is_dependent & has_ssn
+
+    class mt_newborn_credit_eligible(Variable):
+        value_type = bool
+        entity = TaxUnit
+        label = "Eligible for the Montana newborn credit"
+        definition_period = YEAR
+        defined_for = StateCode.MT
+
+        def formula(tax_unit, period, parameters):
+            has_earned_income = tax_unit("tax_unit_earned_income", period) > 0
+            has_qualifying_children = (
+                add(
+                    tax_unit,
+                    period,
+                    ["mt_newborn_credit_eligible_child"],
+                )
+                > 0
+            )
+            person = tax_unit.members
+            head_or_spouse = person("is_tax_unit_head_or_spouse", period)
+            has_ssn = person("meets_eitc_identification_requirements", period)
+            # Uses any() not all(): at least one filer needs SSN,
+            # unlike EITC which requires all filers to have SSN.
+            filer_has_ssn = tax_unit.any(head_or_spouse & has_ssn)
+            return has_earned_income & has_qualifying_children & filer_has_ssn
+
+    class mt_newborn_credit(Variable):
+        value_type = float
+        entity = TaxUnit
+        label = "Montana newborn credit"
+        definition_period = YEAR
+        unit = USD
+        defined_for = "mt_newborn_credit_eligible"
+
+        def formula(tax_unit, period, parameters):
+            p = parameters(period).gov.contrib.states.mt.newborn_credit
+            qualifying_children = add(
+                tax_unit, period, ["mt_newborn_credit_eligible_child"]
+            )
+            base_credit = p.amount * qualifying_children
+            filing_status = tax_unit("filing_status", period)
+            agi = tax_unit("adjusted_gross_income", period)
+            threshold = p.reduction.threshold[filing_status]
+            excess = max_(agi - threshold, 0)
+            # Ceiling: any fraction of an increment triggers reduction
+            increments = np.ceil(excess / p.reduction.increment)
+            reduction = p.reduction.amount * increments
+            return max_(base_credit - reduction, 0)
+
+    def modify_parameters(parameters):
+        # NOTE: MT CTC reform hard-codes the refundable credits list,
+        # so this reform must run after MT CTC in reforms.py to
+        # correctly append mt_newborn_credit via read-then-append.
+        refundable = parameters.gov.states.mt.tax.income.credits.refundable
+        current_refundable = refundable(instant("2027-01-01"))
+        if "mt_newborn_credit" not in current_refundable:
+            new_refundable = list(current_refundable) + ["mt_newborn_credit"]
+            refundable.update(
+                start=instant("2027-01-01"),
+                stop=instant("2100-12-31"),
+                value=new_refundable,
+            )
+        return parameters
+
+    class reform(Reform):
+        def apply(self):
+            self.update_variable(mt_newborn_credit_eligible_child)
+            self.update_variable(mt_newborn_credit_eligible)
+            self.update_variable(mt_newborn_credit)
+            self.modify_parameters(modify_parameters)
+
+    return reform
+
+
+def create_mt_newborn_credit_reform(parameters, period, bypass: bool = False):
+    if bypass:
+        return create_mt_newborn_credit()
+
+    p = parameters.gov.contrib.states.mt.newborn_credit
+
+    reform_active = False
+    current_period = period_(period)
+
+    for _ in range(5):
+        if p(current_period).in_effect:
+            reform_active = True
+            break
+        current_period = current_period.offset(1, "year")
+
+    if reform_active:
+        return create_mt_newborn_credit()
+    else:
+        return None
+
+
+mt_newborn_credit = create_mt_newborn_credit_reform(None, None, bypass=True)