Gate the Child Tax Credit child element on eligibility

changelog.d/2594.fixed.md

@@ -0,0 +1 @@
+- Exclude the Child Tax Credit child element for ineligible families so phantom tax credit income does not reduce Housing Benefit or Council Tax Reduction.

policyengine_uk/parameters/gov/dwp/tax_credits/README.md

@@ -1 +1,19 @@
 # Tax Credits
+
+The model includes the child, family and disability elements in the Child Tax
+Credit maximum only when `is_CTC_eligible` is true. [Sections 8 and 9 of the Tax
+Credits Act 2002](https://www.legislation.gov.uk/ukpga/2002/21/section/8)
+set the entitlement and maximum-rate framework; [section 9](https://www.legislation.gov.uk/ukpga/2002/21/section/9)
+provides the elements of that maximum.
+
+`would_claim_CTC` records whether the family would claim an eligible award. It
+does not establish eligibility. The existing legacy-claim eligibility rule uses
+reported Child Tax Credit and excludes Universal Credit claimants and families
+whose legacy benefits have closed. A family that would claim but fails that
+rule has no Child Tax Credit maximum to enter the tax credit income calculation.
+
+`tax_credits` combines the pre-minimum Child Tax Credit and Working Tax Credit
+awards and applies the shared minimum-payment rule. Housing Benefit and Council
+Tax Reduction read this combined award as income. Gating each element prevents
+an ineligible family's child element from reducing those benefits through tax
+credit income that the family does not receive.

policyengine_uk/tests/policy/baseline/finance/benefit/claimant_not_own_child_or_qualifying_young_person.yaml

@@ -125,13 +125,16 @@
         age: 40
         is_parent: true
         is_claimant_or_partner: true
+        # Continuing CTC claim; this fixture does not claim Universal Credit.
+        child_tax_credit_reported: 1_000
       young_person:
         age: 17
         current_education: UPPER_SECONDARY
         is_claimant_or_partner: false
     benunits:
       benunit:
         members: [parent, young_person]
+        would_claim_uc: false
   output:
     is_child_or_qualifying_young_person_for_child_tax_credit: [false, true]
     is_responsible_for_child_or_qualifying_young_person_for_child_tax_credit: true
@@ -147,12 +150,15 @@
         current_education: UPPER_SECONDARY
         is_parent: true
         is_claimant_or_partner: true
+        # Continuing CTC claim; this fixture does not claim Universal Credit.
+        child_tax_credit_reported: 1_000
       baby:
         age: 1
         is_claimant_or_partner: false
     benunits:
       benunit:
         members: [parent, baby]
+        would_claim_uc: false
   output:
     is_child_or_qualifying_young_person_for_child_tax_credit: [false, true]
     CTC_child_element: 3_455

policyengine_uk/tests/policy/baseline/finance/benefit/family/tax_credits.yaml

@@ -129,6 +129,8 @@
     people:
       parent:
         age: 35
+        # A reported award represents an eligible continuing CTC claim.
+        child_tax_credit_reported: 1000
       child_1:
         age: 10
         date_of_birth: 20140301
@@ -141,6 +143,7 @@
     benunits:
       benunit:
         members: [parent, child_1, child_2, child_3]
+        would_claim_uc: false
   output:
     CTC_child_element: 10_365
 - name: CTC child element for a third child born 6 April 2017
@@ -150,6 +153,8 @@
     people:
       parent:
         age: 35
+        # A reported award represents an eligible continuing CTC claim.
+        child_tax_credit_reported: 1000
       child_1:
         age: 10
         date_of_birth: 20140301
@@ -162,5 +167,6 @@
     benunits:
       benunit:
         members: [parent, child_1, child_2, child_3]
+        would_claim_uc: false
   output:
     CTC_child_element: 6_910