Add Universal Credit capital limits (#1572)

* Add Universal Credit capital limits

* Refine UC capital treatment

* Tighten UC capital modeling

* Model Universal Credit capital limits

* Format UC capital helper variables

* Update UC taper reform regression target

Author: MaxGhenis

policyengine_uk/parameters/gov/dwp/universal_credit/means_test/capital/lower_threshold.yaml

@@ -0,0 +1,10 @@
+description: Universal Credit lower capital threshold.
+values:
+  2013-04-29: 6_000
+metadata:
+  label: Universal Credit lower capital threshold
+  period: year
+  unit: currency-GBP
+  reference:
+    - title: The Universal Credit Regulations 2013 reg. 72
+      href: https://www.legislation.gov.uk/uksi/2013/376/regulation/72

policyengine_uk/parameters/gov/dwp/universal_credit/means_test/capital/sources.yaml

@@ -0,0 +1,39 @@
+description: >
+  Model variables currently mapped to countable Universal Credit capital.
+  Regulation 46 takes the whole of a person's capital into account unless it is
+  treated as income or disregarded under regulation 48 and Schedule 10. The
+  current mappings are `savings` for liquid capital,
+  `other_residential_property_value` for residential property other than the
+  home, `non_residential_property_value` for other land and premises, and
+  `corporate_wealth` for shares and similar investment assets. `main_residence_value`
+  is excluded because Schedule 10 paragraph 1 disregards premises occupied as
+  the person's home. Other Schedule 10 disregards within these broad asset
+  classes are not yet split out separately. Where only household-level capital
+  is available for a multi-benunit household, the model uses a household-wide
+  adult-share proxy for residual capital because the dataset does not identify
+  which adults hold the beneficial interest in each capital asset. The
+  denominator is all unreported adults in the household, including adults in
+  benunits that are not themselves UC claimants. That proxy is a data
+  approximation, not a legislated allocation rule. Regulation 47 is cited only
+  as related context on jointly held capital. If some benunits provide
+  `uc_reported_capital`, the proxy is applied only to the residual household
+  capital for benunits that remain unreported.
+metadata:
+  label: Universal Credit countable capital sources
+  period: year
+  unit: list
+  reference:
+    - title: The Universal Credit Regulations 2013 reg. 46(1)
+      href: https://www.legislation.gov.uk/uksi/2013/376/regulation/46/1
+    - title: The Universal Credit Regulations 2013 reg. 47
+      href: https://www.legislation.gov.uk/uksi/2013/376/regulation/47
+    - title: The Universal Credit Regulations 2013 reg. 48(1)
+      href: https://www.legislation.gov.uk/uksi/2013/376/regulation/48/1
+    - title: The Universal Credit Regulations 2013 Schedule 10 para. 1
+      href: https://www.legislation.gov.uk/uksi/2013/376/schedule/10/paragraph/1
+values:
+  2013-04-29:
+    - savings
+    - other_residential_property_value
+    - non_residential_property_value
+    - corporate_wealth

policyengine_uk/parameters/gov/dwp/universal_credit/means_test/capital/tariff_income/amount.yaml

@@ -0,0 +1,10 @@
+description: Universal Credit monthly tariff income for each capital step above the lower threshold.
+values:
+  2013-04-29: 4.35
+metadata:
+  label: Universal Credit monthly tariff income per capital step
+  period: month
+  unit: currency-GBP
+  reference:
+    - title: The Universal Credit Regulations 2013 reg. 72
+      href: https://www.legislation.gov.uk/uksi/2013/376/regulation/72

policyengine_uk/parameters/gov/dwp/universal_credit/means_test/capital/tariff_income/step.yaml

@@ -0,0 +1,10 @@
+description: Capital step used to calculate Universal Credit tariff income.
+values:
+  2013-04-29: 250
+metadata:
+  label: Universal Credit capital step for tariff income
+  period: year
+  unit: currency-GBP
+  reference:
+    - title: The Universal Credit Regulations 2013 reg. 72
+      href: https://www.legislation.gov.uk/uksi/2013/376/regulation/72

policyengine_uk/parameters/gov/dwp/universal_credit/means_test/capital/upper_threshold.yaml

@@ -0,0 +1,10 @@
+description: Universal Credit upper capital threshold.
+values:
+  2013-04-29: 16_000
+metadata:
+  label: Universal Credit upper capital threshold
+  period: year
+  unit: currency-GBP
+  reference:
+    - title: The Universal Credit Regulations 2013 reg. 18
+      href: https://www.legislation.gov.uk/uksi/2013/376/regulation/18

policyengine_uk/parameters/gov/dwp/universal_credit/means_test/income_definitions/capital_derived.yaml

@@ -0,0 +1,30 @@
+description: >
+  Model income variables treated as capital-derived income for Universal Credit
+  when tariff income applies. Regulation 72(3) covers actual income derived
+  from capital, for example rental, interest or dividends. In the current
+  model, those map to `property_income` when countable property capital is
+  present, `savings_interest_income` when savings are present, and
+  `dividend_income` when corporate wealth is present. Those linked income
+  streams are removed from `uc_unearned_income` once `uc_tariff_income`
+  applies to avoid double counting the same capital. The model does not add
+  annual income flows back into `uc_assessable_capital`, because the dataset
+  does not identify whether those receipts are retained as capital within the
+  assessment year. When benunit-level `uc_reported_capital` is provided, the
+  model treats that as sufficient evidence of countable capital for all listed
+  capital-derived income variables, so `savings_interest_income`,
+  `dividend_income`, and `property_income` are all suppressed once tariff
+  income applies.
+metadata:
+  economy: false
+  label: Universal Credit capital-derived unearned income sources
+  propagate_metadata_to_children: true
+  period: year
+  unit: list
+  reference:
+    - title: The Universal Credit Regulations 2013 reg. 72(3)
+      href: https://www.legislation.gov.uk/uksi/2013/376/regulation/72/3
+values:
+  2013-04-29:
+    - savings_interest_income
+    - dividend_income
+    - property_income

policyengine_uk/parameters/gov/dwp/universal_credit/means_test/income_definitions/unearned.yaml

@@ -6,15 +6,18 @@ metadata:
   period: year
   unit: list
   reference:
-    - title: The Universal Credit Regulations 2013 sec. 66.
-      href: https://www.legislation.gov.uk/uksi/2013/376/data.pdf#page=64
+    - title: The Universal Credit Regulations 2013 reg. 66
+      href: https://www.legislation.gov.uk/uksi/2013/376/regulation/66
+    - title: The Universal Credit Regulations 2013 reg. 72
+      href: https://www.legislation.gov.uk/uksi/2013/376/regulation/72
 
 
 values:
-  2010-01-01:
+  2013-04-29:
   - carers_allowance
   - jsa_contrib
   - private_pension_income
+  - uc_tariff_income
   - savings_interest_income
   - dividend_income
   - property_income

policyengine_uk/tests/microsimulation/reforms_config.yaml

@@ -20,7 +20,7 @@ reforms:
   parameters:
     gov.hmrc.child_benefit.amount.additional: 25
 - name: Reduce Universal Credit taper rate to 20%
-  expected_impact: -41.9
+  expected_impact: -18.1
   tolerance: 3.0
   parameters:
     gov.dwp.universal_credit.means_test.reduction_rate: 0.2

policyengine_uk/tests/policy/baseline/finance/benefit/family/universal_credit/income/uc_income_reduction.yaml

@@ -27,3 +27,22 @@
     uc_maximum_amount: 5_000
   output:
     uc_income_reduction: 950
+
+- name: Capital tariff income reduces Universal Credit
+  period: 2025
+  absolute_error_margin: 0.01
+  input:
+    people:
+      person:
+        age: 30
+    benunits:
+      benunit:
+        uc_earned_income: 0
+        uc_maximum_amount: 5_000
+        members: person
+    households:
+      household:
+        members: person
+        savings: 6_300
+  output:
+    uc_income_reduction: 8.70 * 12

policyengine_uk/tests/policy/baseline/finance/benefit/family/universal_credit/income/uc_tariff_income.yaml

@@ -0,0 +1,50 @@
+- name: No tariff income below the lower capital threshold
+  period: 2025
+  absolute_error_margin: 0
+  input:
+    people:
+      person:
+        age: 30
+    benunits:
+      benunit:
+        members: person
+    households:
+      household:
+        members: person
+        savings: 6_000
+  output:
+    uc_tariff_income: 0
+
+- name: Tariff income rounds capital up to the next step
+  period: 2025
+  absolute_error_margin: 0.01
+  input:
+    people:
+      person:
+        age: 30
+    benunits:
+      benunit:
+        members: person
+    households:
+      household:
+        members: person
+        savings: 6_001
+  output:
+    uc_tariff_income: 4.35 * 12
+
+- name: Tariff income applies through the upper capital limit
+  period: 2025
+  absolute_error_margin: 0.01
+  input:
+    people:
+      person:
+        age: 30
+    benunits:
+      benunit:
+        members: person
+    households:
+      household:
+        members: person
+        savings: 16_000
+  output:
+    uc_tariff_income: 40 * 4.35 * 12