Gate Savings Credit on Pension Credit eligibility

changelog.d/2121.fixed.md

@@ -0,0 +1 @@
+- Applied the shared Pension Credit eligibility conditions to computed Savings Credit amounts.

policyengine_uk/tests/policy/baseline/gov/dwp/pension_credit/savings_credit/savings_credit.yaml

@@ -2,6 +2,7 @@
   period: 2026
   absolute_error_margin: 0.01
   input:
+    age: 80
     is_savings_credit_eligible: true
     relation_type: SINGLE
     savings_credit_income: 20_000
@@ -15,6 +16,7 @@
   period: 2026
   absolute_error_margin: 0.01
   input:
+    age: 80
     is_savings_credit_eligible: true
     relation_type: SINGLE
     savings_credit_income: 20_000

policyengine_uk/tests/test_savings_credit_eligibility.py

@@ -0,0 +1,152 @@
+"""Savings Credit shares Pension Credit eligibility, not just its local age test.
+
+The literal amounts use the existing 2026 model rates. The mixed-age case's
+old positive amount is an off-route diagnostic, not lawful entitlement. The
+positive controls reached pensionable age before April 2016; no protected
+mixed-age Savings Credit continuity is inferred from reported Pension Credit.
+"""
+
+import numpy as np
+import pytest
+
+from policyengine_uk import Simulation
+from policyengine_uk.variables.gov.dwp.pension_credit.savings_credit.savings_credit import (
+    savings_credit,
+)
+
+pytestmark = pytest.mark.usefixtures("cloned_uk_tax_benefit_system")
+YEAR = 2026
+
+
+def situation():
+    units = [
+        ([(80, 20_000, 0), (60, 0, 0)], 6_240),
+        ([(80, 9_000, 0), (78, 9_000, 0)], 6_240),
+        ([(80, 11_000, 2_000)], 7_800),
+        ([(40, 0, 0)], 6_240),
+    ]
+    people, benunits, households = {}, {}, {}
+    for i, (adults, rent) in enumerate(units):
+        names = []
+        for j, (age, pension, private_pension) in enumerate(adults):
+            name = f"p{i}_{j}"
+            names.append(name)
+            people[name] = {
+                "age": {YEAR: age},
+                "is_claimant_or_partner": {YEAR: True},
+                "state_pension": {YEAR: pension},
+                "private_pension_income": {YEAR: private_pension},
+            }
+        benunits[f"b{i}"] = {
+            "members": names,
+            "would_claim_pc": {YEAR: True},
+            "would_claim_housing_benefit": {YEAR: True},
+            "would_claim_uc": {YEAR: False},
+        }
+        households[f"h{i}"] = {
+            "members": names,
+            "country": {YEAR: "ENGLAND"},
+            "local_authority": {YEAR: "MAIDSTONE"},
+            "tenure_type": {YEAR: "RENT_FROM_COUNCIL"},
+            "rent": {YEAR: rent},
+            "council_tax": {YEAR: 2_000},
+            "savings": {YEAR: 0},
+        }
+    return {"people": people, "benunits": benunits, "households": households}
+
+
+def ungated_simulation():
+    """Retain the former amount formula for a downstream differential control."""
+    sim = Simulation(situation=situation())
+    sim.tax_benefit_system.update_variable(
+        type("savings_credit", (savings_credit,), {"defined_for": None})
+    )
+    return sim
+
+
+@pytest.mark.parametrize("first", ["savings_credit", "pension_credit"])
+def test_unprotected_mixed_age_savings_credit_is_zero(first):
+    sim = Simulation(situation=situation())
+    sim.calculate(first, YEAR)
+    # The older member meets the local pre-2016 age condition, but the
+    # unprotected younger partner excludes the couple from Pension Credit.
+    assert sim.calculate("is_savings_credit_eligible", YEAR).tolist() == [
+        True,
+        True,
+        True,
+        False,
+    ]
+    assert sim.calculate("is_pension_credit_eligible", YEAR).tolist() == [
+        False,
+        True,
+        True,
+        False,
+    ]
+    # Couple: 0.6 * (18,000 - 329.75*52) = 511.80.
+    # Single: 0.6*(238-208.07)*52 - 0.4*(12,914-238*52) = 718.616.
+    np.testing.assert_allclose(
+        sim.calculate("savings_credit", YEAR),
+        [0, 511.80, 718.616, 0],
+        atol=0.01,
+        rtol=0,
+    )
+
+
+def test_shared_gate_preserves_final_pension_credit_and_consumers():
+    fixed = Simulation(situation=situation())
+    former = ungated_simulation()
+    # The old off-route calculation was 0.6*(18,766-329.75*52) = 971.40, with the default married
+    # couple receiving the existing Marriage Allowance of 1,260.
+    assert former.calculate("savings_credit", YEAR)[0] == pytest.approx(
+        971.40, abs=0.01
+    )
+    assert fixed.calculate("savings_credit", YEAR)[0] == 0
+    consumers = [
+        "guarantee_credit",
+        "pension_credit_entitlement",
+        "pension_credit",
+        "in_receipt_of_savings_credit_only",
+        "housing_benefit_applicable_income",
+        "housing_benefit_assessable_capital",
+        "housing_benefit_tariff_income",
+        "housing_benefit",
+        "council_tax_reduction_applicable_income",
+        "council_tax_reduction_assessable_capital",
+        "council_tax_reduction",
+        "targeted_childcare_entitlement",
+    ]
+    for variable in consumers:
+        np.testing.assert_allclose(
+            fixed.calculate(variable, YEAR),
+            former.calculate(variable, YEAR),
+            atol=0.01,
+            rtol=0,
+            err_msg=variable,
+        )
+    # Both-old couple: Guarantee Credit 18,889-18,000 = 889, plus 511.80.
+    for variable in ("pension_credit_entitlement", "pension_credit"):
+        np.testing.assert_allclose(
+            fixed.calculate(variable, YEAR),
+            [0, 1_400.80, 718.616, 0],
+            atol=0.01,
+            rtol=0,
+        )
+    # The couple gets full rent on Guarantee Credit. The single's HB is
+    # 7,800 - 0.65*(12,914+718.616-256*52) = 7,591.5996.
+    np.testing.assert_allclose(
+        fixed.calculate("housing_benefit", YEAR),
+        [0, 6_240, 7_591.5996, 0],
+        atol=0.01,
+        rtol=0,
+    )
+
+
+def test_direct_savings_credit_input_keeps_its_existing_override_behavior():
+    data = situation()
+    data["benunits"]["b0"]["savings_credit"] = {YEAR: 123}
+    sim = Simulation(situation=data)
+    assert sim.calculate("savings_credit", YEAR)[0] == 123
+    # An explicitly supplied component does not create a Pension Credit award.
+    assert sim.calculate("pension_credit_entitlement", YEAR)[0] == 0
+    assert sim.calculate("pension_credit", YEAR)[0] == 0
+    assert sim.calculate("housing_benefit", YEAR)[0] == 0

policyengine_uk/variables/gov/dwp/pension_credit/savings_credit/savings_credit.py

@@ -8,6 +8,13 @@ class savings_credit(Variable):
     value_type = float
     unit = GBP
     reference = "https://www.legislation.gov.uk/ukpga/2002/16/section/3"
+    documentation = (
+        "The savings credit element of State Pension Credit, zero unless the "
+        "benefit unit meets the shared Pension Credit entitlement conditions. "
+        "This is the computed component before Pension Credit take-up; a "
+        "positive amount does not by itself establish an award in payment."
+    )
+    defined_for = "is_pension_credit_eligible"
 
     def formula(benunit, period, parameters):
         income = benunit("savings_credit_income", period)