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Stop the statutory Marriage Allowance rate from switching on the CPS expanded Marriage Allowance - #2553

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Oct 23, 2026
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Stop the statutory Marriage Allowance rate from switching on the CPS expanded Marriage Allowance#2553
MaxGhenis merged 2 commits into
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fix/ma-cps-trigger-2551

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@MaxGhenis MaxGhenis commented Oct 21, 2026 •
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Fixes #2551

What was wrong

create_marriage_tax_reform (policyengine_uk/reforms/cps/marriage_tax_reforms.py) adds the CPS expanded Marriage Allowance to every simulation whose parameters switch it on. The switch was remove_income_condition or rate != original_rate. Here rate is gov.contrib.cps.marriage_tax_reforms.expanded_ma.ma_rate (default 0.1) and original_rate is the statutory gov.hmrc.income_tax.allowances.marriage_allowance.max, so any change to the statutory rate switched the reform on. With max_child_age at its default 0, the reform's meets_expanded_ma_conditions is true for everyone. It then admits the higher and additional bands and caps every transfer at ma_rate, ignoring the statutory rate. A statutory rate of 0 therefore kept a 10% allowance for basic-rate couples and gave one to higher-rate couples. Raising the statutory rate to 20% also left basic-rate couples at 10%.

The fix

The reform now switches on from its own parameters only: remove_income_condition, or an ma_rate other than its unreformed value. The unreformed value is read from parameters.baseline, the unreformed copy that adjust_budgets and baseline_vat already compare against. On every reform route below I checked that parameters.baseline holds 0.1 when the switch runs, whatever the reform sets. Nothing inside the reform changes. People outside its conditions (with a max_child_age) keep the statutory rate, as before, and a test now covers that.

Why not a new in_effect flag

Other UK structural reforms switch on from a boolean (gov.contrib.conservatives.cb_hitc_household, gov.contrib.policyengine.disable_simulated_benefits, gov.contrib.scotland.scottish_child_payment.in_effect), or compare a parameter with parameters.baseline (adjust_budgets). The expanded Marriage Allowance already has a boolean switch, remove_income_condition. With ma_rate at its default, an in_effect flag would build exactly the reform that remove_income_condition builds.

Searching for expanded_ma and marriage_tax_reforms:

  • policyengine-app-v2, policyengine-api, policyengine-api-v2 and policyengine-api-v2-alpha (git grep at origin HEAD): no references.
  • Org-wide GitHub code search found policyengine.py and policyengine-scorecard. policyengine.py's budget_reform_contract.py uses remove_income_condition as its structural-switch case, which still works. policyengine-scorecard has only replay result packets.
  • app-v2's parameter search reaches gov.contrib.* behind its includeContrib filter, so saved policies may set ma_rate. Those policies still switch the reform on, because the rate differs from its default.

The only saved policies that change are ones that moved the statutory rate:

  • Statutory rate alone: these now get the statutory result, which is the fix.
  • Both rates set to the same non-default value (for example 0.2): these used to leave the reform off and now switch it on, because the CPS rate changed.
  • A policy that relied on a statutory change to run the reform at its default 10% (for example statutory 0 with max_child_age 5) now needs remove_income_condition: true.

Tests

The switch runs when policyengine_uk.Simulation is built. YAML policy tests build simulations with core's SimulationBuilder, which never runs the parameter-switched structural reforms. So the reproducers are Python tests, and they run on each route a parameter change takes: a reform dict, Scenario(parameter_changes=...), Reform.from_dict, and Scenario with applied_before_data_load.

Reproducer: policyengine_uk/tests/test_marriage_allowance_cps_switch.py::test_a_zero_statutory_rate_removes_the_allowance, policyengine_uk/tests/test_marriage_allowance_cps_switch.py::test_a_higher_statutory_rate_raises_only_the_statutory_allowance, policyengine_uk/tests/test_marriage_allowance_cps_switch.py::test_a_zero_statutory_rate_is_no_allowance_for_anyone, policyengine_uk/tests/test_marriage_allowance_cps_switch.py::test_the_reform_switches_on_from_its_own_parameters_only

The issue's couples, computed by hand from the 2025-26 parameters (£12,570 personal allowance; 20% on the first £37,700, then 40%). The YAML cases are in policyengine_uk/tests/policy/baseline/gov/hmrc/income_tax/allowances/marriage_allowance_statutory_rate.yaml, and the Python tests repeat them through Simulation:

Couple Statutory rate marriage_allowance (earner, partner) Earner's income_tax On main
£30,000 earner 10% (current law) 1,260, 0 3,234 same
£30,000 earner 0 0, 0 3,486 (+252) 1,260 and 3,234
£30,000 earner 20% 2,520, 0 2,982 1,260 and 3,234
£60,000 earner 10% (current law) 0, 0 11,432 same
£60,000 earner 0 0, 0 11,432 1,260 and 10,928
£60,000 earner 20% 0, 0 11,432 1,260 and 10,928

Regression cases (invariant 5): remove_income_condition and ma_rate = 0.2 still switch the reform on, on every route, with the values main gives. With ma_rate = 0.2 and max_child_age = 5, couples without a child under 5 keep the statutory allowance (1,260 at current law, 0 at a statutory 0), and couples with one get 2,520.

Invariants

Each is stated for every input and tested with Hypothesis.

  1. Switch. The reform is on exactly when remove_income_condition is true or ma_rate differs from its unreformed value. The statutory rate has no effect. This is tested over random statutory rates, CPS rates, switches and child ages. At the statutory rate in force it is identical to the old switch, and at current law the reform is off in every year from 2016 to 2035.
  2. Abolition. With the statutory rate at 0 and the CPS parameters at their defaults, marriage_allowance is 0 for every person. Income tax then equals current-law income tax when no one claims the allowance.
  3. Statutory bounds. With any statutory rate and the CPS parameters at their defaults, no one in a band outside eligible_bands (which includes everyone in the higher and additional bands) meets meets_marriage_allowance_income_conditions or has an allowance. No one's allowance exceeds 12,570 × rate rounded up to the next £10. Rates are drawn in whole thousandths, so the bound is exact; the test file comment explains why.
  4. Monotonicity. marriage_allowance never falls when the statutory rate rises.
  5. Regression. Switched on by remove_income_condition, the reform gives the same marriage_allowance, income conditions and income_tax as the explicit expanded_ma_reform for every generated couple.

The generated couples: 20 per simulation, drawn incomes including values near the UK and Scottish band edges, married or not, each partner claiming or not. A quarter of them live in Scotland.

Run locally

A host reservation was in force, so everything ran single-process and without microsimulation tests. CI runs the full suite.

  • New Python tests: 45 passed (128 s).
  • The same file against main's marriage_tax_reforms.py: the 12 reproducer tests fail (the zero and 20% statutory-rate cases on all four routes, the CPS-rate case, invariants 1, 2 and 3) and the other 33 pass.
  • policyengine-core test on policyengine_uk/tests/policy/baseline/gov/hmrc/income_tax and policyengine_uk/tests/policy/reforms/cps: 334 passed.
  • test_reform_representations.py, test_dated_reform_routes.py::test_a_dict_reform_switches_on_a_parameter_gated_structural_reform and test_labour_supply_couples.py: 103 passed.
  • ruff format --check . and ruff check .: clean.

Impact

Current law should be exactly unchanged. At baseline the statutory rate equals ma_rate, so the old switch was off too, and the reform's variables are untouched. Aggregate impact report: pending (CI).

Reforms that change the statutory rate do change. Abolishing the allowance now raises income tax: on the issue's couples, +£252 for the basic-rate earner and nothing for the higher-rate one. Before, it gave the higher-rate one £504 off. The policyengine-scorecard as2013_marriage_allowance rerun on this branch is pending.

Overlapping pull requests

axiom: n/a: this changes when a contributed (CPS) reform switches on, not a statutory provision; the statutory Marriage Allowance rules (ITA 2007 ss. 55B–55C) are unchanged

🤖 Generated with Claude Code

MaxGhenis and others added 2 commits October 21, 2026 14:40
@MaxGhenis @claude
Switch the CPS expanded Marriage Allowance on from its own parameters…
bfd322a 
… only

create_marriage_tax_reform built the expanded Marriage Allowance whenever
the CPS ma_rate differed from the statutory Marriage Allowance rate. A
change to the statutory rate therefore switched the reform on: setting it
to 0 replaced it with the CPS 10% rate and, with no child-age condition,
opened the allowance to higher- and additional-rate taxpayers.

Compare ma_rate with its own unreformed value (parameters.baseline, as
adjust_budgets does) instead. remove_income_condition still switches the
reform on by itself.

Fixes #2551

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
@MaxGhenis @claude
Test that the statutory Marriage Allowance rate leaves the CPS reform…
3883005 
… off

The switch runs when policyengine_uk.Simulation is built, which YAML policy
tests skip, so the reproducers are Python tests on every reform route:

- a statutory rate of 0 removes the allowance (the £30,000 earner pays 252
  more; the £60,000 earner the same), and 20% raises only the statutory
  allowance;
- remove_income_condition or an ma_rate change still switch the reform on,
  with the values main gave;
- couples outside the reform's child condition keep the statutory rate.

Hypothesis properties cover the switch itself over random parameter values,
a zero statutory rate giving no allowance and the same income tax as no
claims, the band and £10-rounded cap bounds at any statutory rate,
monotonicity in the statutory rate, and the switched-on reform matching
the explicit expanded_ma_reform. YAML cases pin the issue's hand-computed
2025-26 values.

On main's create_marriage_tax_reform, 12 of the 45 new Python tests fail
(the reproducers); the rest pass.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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github-actions Bot commented Oct 21, 2026 •
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Aggregate impact on certified data: pass

Base ecd531776e against head 9bbd024f18, both on enhanced_frs_2024_25.h5 (policyengine-uk-data 1.58.1, sha256 056e80fd8e91), fiscal years 2025-26 to 2031-32. Each year is a full microsimulation run on each side.

Checks: 0 broken by this change, 1 failing on both sides, 0 fixed. Moves flagged for review: 0 (thresholds in report_spec.yaml; a flag does not fail the job).

Workflow run and full report

Notes

  • In the years a figure from fewer than 10 records is suppressed (spending.disabled_students_allowance), every total containing it, and the decile incomes, are rebuilt from their other components, so no published total includes it. Those totals are marked †. A change is withheld where the two sides leave out different figures and can't be lined up.

Moves flagged for review

None.

Spending by benefit and service

Measure 2025-26 2026-27 2027-28 2028-29 2029-30 2030-31 2031-32
Disabled Students' Allowance suppressed suppressed suppressed suppressed suppressed suppressed suppressed

Caseloads

Measure 2025-26 2026-27 2027-28 2028-29 2029-30 2030-31 2031-32
Disabled Students' Allowance suppressed suppressed suppressed suppressed suppressed suppressed suppressed

Household net income by decile

No household's net income changes in any year.

No change in any year: receipts by tax head; government balance, each component counted once; model totals; components the model counts twice; household income totals; population; poverty rates; people in poverty; inequality; mean household net income in each side's own deciles; standard reform costings (change in gov_balance); standard reforms: change in each reform's target.

Checks failing on both base and head (1)
  • VAT is never negative (sign:vat): 2025-26: 76 units below zero, a weighted £-54,797,972 in total; 2026-27: 76 units below zero, a weighted £-56,271,349 in total; 2027-28: 76 units below zero, a weighted £-57,609,146 in total
Counted-once check

Each of 84 components was raised by £1 per unit in 2026-27, and every head of its totals was read household by household: its own head must rise by exactly £1, no other tax head may move, no other benefit may rise, and the model's own total must move by what its heads moved. A head that breaks a rule is measured again twice: with every other head held at its baseline value, and with every other head held at its value after the first £1 while the component rises again. It fails where either still shows the response. 0 failed; 0 were skipped.

Provenance
Side Commit Runtime Environment hash Partition hash Time
base main ecd531776e uk 2.145.0 (files e09a3aa74820), core 3.33.2, py 3.13.16 aarch64 ccab9aa7a280 f210f83d5be4 1499.34s
head #2553 merged into main 9bbd024f18 uk 2.145.0 (files 40d4edf9e69b), core 3.33.2, py 3.13.16 aarch64 ccab9aa7a280 f210f83d5be4 1545.8s

Dataset: hf://policyengine/policyengine-uk-data-private/enhanced_frs_2024_25.h5@2526edbbb687a3b54dbb11272e5389e4b62d2ac2, sha256 056e80fd8e9151d78f432a25cde863340baee81304c6216a37fb575ce8563784 (verified on both sides), policyengine-uk-data 1.58.1.

Receipts by tax head: head levels
Measure (head) 2025-26 2026-27 2027-28 2028-29 2029-30 2030-31 2031-32
Income tax £299.36bn £319.12bn £336.63bn £351.79bn £367.34bn £385.47bn £403.77bn
National Insurance (employee and self-employed) £52.58bn £54.94bn £56.75bn £58.48bn £60.62bn £62.57bn £65.03bn
National Insurance (employer) £152.64bn £159.18bn £164.14bn £168.73bn £176.11bn £181.72bn £188.90bn
Employer NI change borne by capital £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn
Employer NI change borne by consumers £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn
Capital gains tax £12.62bn £13.06bn £13.55bn £14.04bn £14.54bn £15.09bn £15.65bn
Student loan repayments £7.83bn £8.12bn £8.35bn £8.56bn £8.79bn £9.04bn £9.38bn
VAT £253.71bn £260.53bn £266.72bn £273.14bn £279.83bn £286.71bn £293.71bn
Change in VAT from its baseline £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn
VAT on private school fees £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn
Fuel duties £24.53bn £24.64bn £26.64bn £26.69bn £26.42bn £25.76bn £26.35bn
Alcohol duties £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn
Tobacco duties £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn
Vehicle excise duties £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn
TV licence fee £4.28bn £4.43bn £4.44bn £4.46bn £4.49bn £4.51bn £4.53bn
Council tax £49.56bn £52.45bn £55.78bn £59.39bn £62.98bn £66.74bn £70.70bn
High value council tax surcharge £0.00bn £0.00bn £0.00bn £0.48bn £0.49bn £0.51bn £0.52bn
Northern Ireland domestic rates £0.55bn £0.58bn £0.61bn £0.63bn £0.67bn £0.70bn £0.73bn
Business rates £31.73bn £31.73bn £31.73bn £31.73bn £31.73bn £31.73bn £31.73bn
Stamp duty land tax (own purchases, and corporate until the £10.06bn £10.56bn £10.98bn £11.40bn £11.81bn £12.23bn £12.64bn
Land transaction tax (Wales) £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn
Land and buildings transaction tax (Scotland) £0.01bn £0.01bn £0.02bn £0.02bn £0.02bn £0.02bn £0.02bn
Unspecified tax change borne by capital £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn
Unspecified tax change borne by consumers £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn
Wealth tax £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn
Wealth tax excluding the main residence £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn
Land value tax £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn
Carbon tax £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn
Spending by benefit and service: head levels
Measure (head) 2025-26 2026-27 2027-28 2028-29 2029-30 2030-31 2031-32
State Pension £122.50bn £127.12bn £128.28bn £130.21bn £134.05bn £138.02bn £142.08bn
Pension Credit £6.66bn £7.04bn £7.02bn £7.09bn £7.21bn £7.34bn £7.44bn
Winter Fuel Payment £1.70bn £1.68bn £1.59bn £1.57bn £1.57bn £1.55bn £1.52bn
Pension Age Winter Heating Payment (Scotland) £0.19bn £0.20bn £0.20bn £0.21bn £0.21bn £0.22bn £0.22bn
Universal Credit £78.78bn £83.08bn £84.89bn £86.65bn £87.58bn £88.99bn £90.32bn
Housing Benefit £8.59bn £8.92bn £9.19bn £9.33bn £9.61bn £9.87bn £10.15bn
Council Tax Reduction £1.99bn £2.03bn £2.08bn £2.13bn £2.18bn £2.23bn £2.28bn
Employment and Support Allowance (income-related) £2.12bn £2.18bn £2.23bn £2.28bn £2.33bn £2.39bn £2.45bn
Employment and Support Allowance (contribution-based) £5.22bn £5.36bn £5.49bn £5.62bn £5.76bn £5.90bn £6.04bn
Jobseeker's Allowance (income-based) £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn
Jobseeker's Allowance (contribution-based) £0.29bn £0.30bn £0.30bn £0.31bn £0.32bn £0.33bn £0.33bn
Income Support £0.12bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn
Working Tax Credit £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn
Child Tax Credit £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn
Incapacity Benefit £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn
Personal Independence Payment £27.05bn £28.19bn £28.94bn £29.64bn £30.37bn £31.11bn £31.87bn
Disability Living Allowance £7.52bn £7.83bn £8.04bn £8.24bn £8.44bn £8.65bn £8.86bn
Attendance Allowance £8.71bn £9.08bn £9.32bn £9.55bn £9.78bn £10.02bn £10.26bn
Carer's Allowance £4.50bn £4.69bn £4.81bn £4.93bn £5.05bn £5.17bn £5.29bn
Carer Support Payment (Scotland) £0.35bn £0.37bn £0.38bn £0.39bn £0.40bn £0.41bn £0.41bn
Carer's Allowance Supplement (Scotland) £0.00bn £0.05bn £0.05bn £0.05bn £0.05bn £0.05bn £0.05bn
Severe Disablement Allowance £0.03bn £0.03bn £0.03bn £0.03bn £0.03bn £0.03bn £0.03bn
Industrial Injuries Disablement Benefit £0.51bn £0.52bn £0.53bn £0.54bn £0.56bn £0.57bn £0.59bn
Armed Forces Compensation Scheme £0.61bn £0.62bn £0.64bn £0.65bn £0.67bn £0.69bn £0.70bn
War Widow's or Widower's Pension £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn
Child Benefit £16.23bn £16.91bn £17.32bn £17.73bn £18.16bn £18.60bn £19.04bn
Scottish Child Payment £0.50bn £0.52bn £0.53bn £0.55bn £0.56bn £0.57bn £0.58bn
Two Child Limit Payment (Scotland, counterfactual) £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn
Healthy Start vouchers £0.05bn £0.05bn £0.05bn £0.05bn £0.05bn £0.05bn £0.05bn
Maternity Allowance £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn
Statutory Maternity Pay £3.32bn £3.41bn £3.49bn £3.57bn £3.66bn £3.75bn £3.84bn
Statutory Paternity Pay £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn
Statutory Sick Pay £1.13bn £1.16bn £1.19bn £1.22bn £1.25bn £1.28bn £1.31bn
Sure Start Maternity Grant £0.01bn £0.01bn £0.01bn £0.01bn £0.01bn £0.01bn £0.01bn
Bereavement Support Payment £0.67bn £0.69bn £0.70bn £0.72bn £0.74bn £0.76bn £0.78bn
Tax-Free Childcare £0.55bn £0.56bn £0.57bn £0.58bn £0.60bn £0.61bn £0.59bn
Extended childcare entitlement £2.66bn £3.14bn £3.23bn £3.30bn £3.38bn £3.47bn £3.55bn
Universal childcare entitlement £3.32bn £3.59bn £3.69bn £3.78bn £3.88bn £3.99bn £4.08bn
Targeted childcare entitlement £0.57bn £0.60bn £0.62bn £0.63bn £0.65bn £0.66bn £0.67bn
Care to Learn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn
Childcare Grant £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn
Parents' Learning Allowance £0.20bn £0.20bn £0.20bn £0.20bn £0.20bn £0.20bn £0.20bn
Adult Dependants' Grant £0.06bn £0.06bn £0.04bn £0.04bn £0.04bn £0.04bn £0.04bn
Travel Grant £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn
Disabled Students' Allowance suppressed suppressed suppressed suppressed suppressed suppressed suppressed
16 to 19 Bursary Fund £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn
NHS spending £204.68bn £205.46bn £206.22bn £207.04bn £207.96bn £208.89bn £209.79bn
State education spending £0.02bn £0.02bn £0.02bn £0.02bn £0.02bn £0.02bn £0.02bn
Transport subsidy spending £25.15bn £25.25bn £25.34bn £25.44bn £25.55bn £25.67bn £25.78bn
Cost-of-living support payment £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn
Energy Bills Rebate £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn
Energy Price Guarantee subsidy £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn
Basic income £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn
Disability basic income £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn
Other public spending budget change £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn
Caseloads: head levels
Measure (head) 2025-26 2026-27 2027-28 2028-29 2029-30 2030-31 2031-32
State Pension 11,308k 11,208k 10,906k 10,812k 10,860k 10,908k 10,955k
Pension Credit 1,490k 1,489k 1,477k 1,455k 1,457k 1,454k 1,450k
Winter Fuel Payment 7,091k 7,008k 6,593k 6,509k 6,491k 6,377k 6,242k
Pension Age Winter Heating Payment (Scotland) 806k 807k 807k 805k 809k 812k 816k
Universal Credit 6,371k 6,379k 6,409k 6,419k 6,395k 6,387k 6,371k
Housing Benefit 1,254k 1,252k 1,254k 1,240k 1,244k 1,247k 1,249k
Council Tax Reduction 3,184k 3,210k 3,223k 3,244k 3,261k 3,279k 3,292k
Employment and Support Allowance (income-related) 187k 188k 188k 189k 190k 190k 191k
Employment and Support Allowance (contribution-based) 722k 724k 727k 730k 733k 737k 740k
Jobseeker's Allowance (income-based) 0k 0k 0k 0k 0k 0k 0k
Jobseeker's Allowance (contribution-based) 67k 67k 68k 68k 68k 69k 69k
Income Support 25k 0k 0k 0k 0k 0k 0k
Working Tax Credit 0k 0k 0k 0k 0k 0k 0k
Child Tax Credit 0k 0k 0k 0k 0k 0k 0k
Incapacity Benefit 0k 0k 0k 0k 0k 0k 0k
Personal Independence Payment 3,581k 3,595k 3,608k 3,623k 3,639k 3,655k 3,671k
Disability Living Allowance 1,296k 1,301k 1,306k 1,311k 1,317k 1,323k 1,329k
Attendance Allowance 1,701k 1,708k 1,714k 1,721k 1,729k 1,736k 1,744k
Carer's Allowance 1,038k 1,042k 1,046k 1,050k 1,055k 1,059k 1,064k
Carer Support Payment (Scotland) 81k 82k 82k 82k 83k 83k 83k
Carer's Allowance Supplement (Scotland) 0k 82k 82k 82k 83k 83k 83k
Severe Disablement Allowance 4k 4k 4k 4k 4k 4k 4k
Industrial Injuries Disablement Benefit 137k 138k 139k 139k 140k 140k 141k
Armed Forces Compensation Scheme 94k 94k 94k 95k 95k 95k 96k
War Widow's or Widower's Pension 0k 0k 0k 0k 0k 0k 0k
Child Benefit 8,136k 8,165k 8,185k 8,215k 8,249k 8,282k 8,314k
Scottish Child Payment 352k 354k 355k 356k 357k 358k 357k
Two Child Limit Payment (Scotland, counterfactual) 0k 0k 0k 0k 0k 0k 0k
Healthy Start vouchers 200k 201k 202k 203k 204k 204k 205k
Maternity Allowance 0k 0k 0k 0k 0k 0k 0k
Statutory Maternity Pay 334k 335k 336k 338k 339k 341k 342k
Statutory Paternity Pay 0k 0k 0k 0k 0k 0k 0k
Statutory Sick Pay 182k 183k 183k 184k 185k 186k 186k
Sure Start Maternity Grant 26k 26k 26k 27k 27k 27k 27k
Bereavement Support Payment 98k 98k 99k 99k 100k 100k 101k
Tax-Free Childcare 1,017k 1,028k 1,028k 1,033k 1,034k 1,038k 1,023k
Extended childcare entitlement 665k 671k 675k 677k 682k 686k 687k
Universal childcare entitlement 986k 989k 992k 997k 1,002k 1,013k 1,015k
Targeted childcare entitlement 119k 120k 120k 121k 121k 122k 121k
Care to Learn 0k 0k 0k 0k 0k 0k 0k
Childcare Grant 0k 0k 0k 0k 0k 0k 0k
Parents' Learning Allowance 98k 99k 99k 100k 100k 100k 101k
Adult Dependants' Grant 18k 18k 12k 13k 13k 13k 13k
Travel Grant 0k 0k 0k 0k 0k 0k 0k
Disabled Students' Allowance suppressed suppressed suppressed suppressed suppressed suppressed suppressed
16 to 19 Bursary Fund 0k 0k 0k 0k 0k 0k 0k
Cost-of-living support payment 0k 0k 0k 0k 0k 0k 0k
Energy Bills Rebate 0k 0k 0k 0k 0k 0k 0k
Energy Price Guarantee subsidy 0k 0k 0k 0k 0k 0k 0k
Basic income 0k 0k 0k 0k 0k 0k 0k
Disability basic income 0k 0k 0k 0k 0k 0k 0k
Government balance, each component counted once: head levels
Measure (head) 2025-26 2026-27 2027-28 2028-29 2029-30 2030-31 2031-32
Government receipts, each component once £899.46bn £939.35bn £976.35bn £1,009.56bn £1,045.84bn £1,082.79bn £1,123.66bn
Government spending £536.58bn † £550.91bn † £557.25bn † £564.32bn † £572.87bn † £582.12bn † £591.27bn †
Government balance, each receipt once £362.88bn † £388.44bn † £419.09bn † £445.24bn † £472.97bn † £500.67bn † £532.39bn †
Benefits in household_benefits but not in gov_spending £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn £0.00bn
Model totals: head levels
Measure (head) 2025-26 2026-27 2027-28 2028-29 2029-30 2030-31 2031-32
gov_tax £902.59bn £942.48bn £979.48bn £1,012.69bn £1,048.97bn £1,085.92bn £1,126.79bn
household_tax £496.24bn £522.77bn £548.61bn £570.81bn £593.03bn £617.48bn £644.19bn
pre_budget_change_household_tax £488.42bn £514.65bn £540.26bn £561.77bn £583.75bn £607.94bn £634.29bn
gov_spending £536.58bn † £550.91bn † £557.25bn † £564.32bn † £572.87bn † £582.12bn † £591.27bn †
household_benefits £536.58bn † £550.91bn † £557.25bn † £564.32bn † £572.87bn † £582.12bn † £591.27bn †
gov_balance £366.01bn † £391.57bn † £422.22bn † £448.37bn † £476.10bn † £503.80bn † £535.52bn †
Components the model counts twice: head levels
Measure (head) 2025-26 2026-27 2027-28 2028-29 2029-30 2030-31 2031-32
corporate_sdlt, counted again inside expected_sdlt £3.13bn £3.13bn £3.13bn £3.13bn £3.13bn £3.13bn £3.13bn
Household income totals: head levels
Measure (head) 2025-26 2026-27 2027-28 2028-29 2029-30 2030-31 2031-32
Household market income £1,657.06bn £1,719.25bn £1,771.68bn £1,821.99bn £1,872.88bn £1,930.99bn £2,001.98bn
Household net income £1,658.12bn † £1,706.63bn † £1,738.44bn † £1,772.55bn † £1,808.65bn † £1,850.28bn † £1,902.01bn †
Household net income (HBAI definition) £1,466.68bn £1,513.41bn £1,545.63bn £1,578.61bn £1,612.63bn £1,651.68bn £1,702.11bn
Population: head levels
Measure (head) 2025-26 2026-27 2027-28 2028-29 2029-30 2030-31 2031-32
People 69,514k 69,778k 70,036k 70,316k 70,626k 70,944k 71,249k
Benefit units 35,247k 35,381k 35,512k 35,654k 35,811k 35,972k 36,127k
Households 31,167k 31,285k 31,401k 31,526k 31,665k 31,808k 31,944k
Poverty rates: head levels
Measure (head) 2025-26 2026-27 2027-28 2028-29 2029-30 2030-31 2031-32
Absolute poverty, before housing costs: everyone 15.9% 14.9% 15.5% 15.6% 15.7% 15.8% 15.7%
Absolute poverty, before housing costs: children 23.7% 20.9% 21.6% 21.4% 21.6% 21.8% 21.7%
Absolute poverty, before housing costs: working-age adults 13.8% 13.4% 14.0% 14.1% 14.2% 14.3% 14.3%
Absolute poverty, before housing costs: pensioners 13.7% 13.1% 13.2% 13.4% 13.5% 13.6% 13.6%
Absolute poverty, after housing costs: everyone 21.1% 20.6% 21.3% 21.5% 21.9% 22.2% 22.3%
Absolute poverty, after housing costs: children 32.1% 30.3% 30.9% 31.1% 31.7% 32.3% 32.5%
Absolute poverty, after housing costs: working-age adults 19.6% 19.4% 20.2% 20.4% 20.8% 21.0% 21.0%
Absolute poverty, after housing costs: pensioners 12.7% 12.5% 12.6% 12.9% 13.0% 13.1% 13.4%
Relative poverty, before housing costs: everyone 16.9% 16.4% 16.4% 16.5% 16.6% 16.7% 16.7%
Relative poverty, before housing costs: children 25.6% 23.5% 23.2% 23.2% 23.3% 23.4% 23.4%
Relative poverty, before housing costs: working-age adults 14.4% 14.4% 14.7% 14.8% 14.9% 15.1% 15.0%
Relative poverty, before housing costs: pensioners 14.8% 14.9% 14.1% 14.3% 14.2% 14.2% 14.4%
Relative poverty, after housing costs: everyone 21.7% 21.3% 21.4% 21.5% 21.7% 21.8% 22.0%
Relative poverty, after housing costs: children 33.0% 31.6% 31.2% 31.1% 31.5% 31.6% 32.0%
Relative poverty, after housing costs: working-age adults 20.0% 20.0% 20.3% 20.4% 20.6% 20.8% 20.9%
Relative poverty, after housing costs: pensioners 13.5% 13.1% 12.7% 12.8% 12.7% 12.7% 12.8%
People in poverty: head levels
Measure (head) 2025-26 2026-27 2027-28 2028-29 2029-30 2030-31 2031-32
Absolute poverty, before housing costs: everyone 11,051k 10,427k 10,848k 10,947k 11,079k 11,209k 11,220k
Absolute poverty, before housing costs: children 3,560k 3,141k 3,261k 3,253k 3,298k 3,334k 3,335k
Absolute poverty, before housing costs: working-age adults 5,864k 5,737k 6,070k 6,165k 6,237k 6,315k 6,321k
Absolute poverty, before housing costs: pensioners 1,627k 1,549k 1,517k 1,529k 1,544k 1,561k 1,565k
Absolute poverty, after housing costs: everyone 14,659k 14,362k 14,899k 15,116k 15,444k 15,724k 15,870k
Absolute poverty, after housing costs: children 4,809k 4,556k 4,676k 4,719k 4,835k 4,939k 4,994k
Absolute poverty, after housing costs: working-age adults 8,333k 8,326k 8,775k 8,931k 9,122k 9,275k 9,329k
Absolute poverty, after housing costs: pensioners 1,518k 1,480k 1,449k 1,466k 1,487k 1,509k 1,547k
Relative poverty, before housing costs: everyone 11,760k 11,456k 11,504k 11,625k 11,706k 11,868k 11,916k
Relative poverty, before housing costs: children 3,840k 3,538k 3,514k 3,525k 3,546k 3,582k 3,603k
Relative poverty, before housing costs: working-age adults 6,154k 6,160k 6,365k 6,465k 6,537k 6,651k 6,652k
Relative poverty, before housing costs: pensioners 1,766k 1,758k 1,625k 1,634k 1,623k 1,634k 1,661k
Relative poverty, after housing costs: everyone 15,065k 14,863k 14,993k 15,090k 15,319k 15,490k 15,653k
Relative poverty, after housing costs: children 4,948k 4,756k 4,711k 4,715k 4,798k 4,840k 4,919k
Relative poverty, after housing costs: working-age adults 8,511k 8,559k 8,822k 8,917k 9,070k 9,192k 9,260k
Relative poverty, after housing costs: pensioners 1,605k 1,548k 1,460k 1,458k 1,452k 1,457k 1,475k
Inequality: head levels
Measure (head) 2025-26 2026-27 2027-28 2028-29 2029-30 2030-31 2031-32
Gini coefficient, equivalised HBAI income before housing costs 0.3074 0.3051 0.3065 0.3071 0.3077 0.3083 0.3094
Mean household net income in each side's own deciles: head levels
Measure (head) 2025-26 2026-27 2027-28 2028-29 2029-30 2030-31 2031-32
Decile 1: mean household_net_income per household £17,707 † £17,997 † £17,941 † £17,992 † £18,326 † £18,523 † £18,684 †
Decile 2: mean household_net_income per household £28,362 † £29,049 † £28,672 † £29,013 † £29,373 † £29,779 † £30,332 †
Decile 3: mean household_net_income per household £34,607 † £35,886 † £36,508 † £37,008 † £37,263 † £37,824 † £38,511 †
Decile 4: mean household_net_income per household £39,329 † £40,908 † £41,807 † £42,695 † £43,186 † £43,984 † £45,129 †
Decile 5: mean household_net_income per household £44,871 † £46,147 † £47,077 † £47,609 † £48,379 † £49,251 † £50,073 †
Decile 6: mean household_net_income per household £47,930 † £49,324 † £50,272 † £51,070 † £52,170 † £52,939 † £54,222 †
Decile 7: mean household_net_income per household £56,320 † £57,578 † £58,469 † £59,414 † £60,124 † £61,607 † £63,192 †
Decile 8: mean household_net_income per household £69,250 † £70,361 † £71,635 † £72,869 † £74,327 † £75,790 † £77,563 †
Decile 9: mean household_net_income per household £79,686 † £82,010 † £83,245 † £84,446 † £86,085 † £87,570 † £90,640 †
Decile 10: mean household_net_income per household £117,623 † £120,464 † £122,413 † £124,563 † £126,773 † £129,082 † £131,885 †
Standard reform costings (change in gov_balance): head levels
Measure (head) 2025-26 2026-27 2027-28 2028-29 2029-30 2030-31 2031-32
Raise basic rate by 1pp £6.22bn £6.50bn £6.71bn £6.90bn £7.11bn £7.35bn £7.62bn
Raise higher rate by 1pp £3.54bn £3.82bn £4.05bn £4.27bn £4.49bn £4.76bn £4.96bn
Raise personal allowance by ~800GBP/year £-3.83bn £-3.96bn £-4.03bn £-4.10bn £-4.20bn £-4.30bn £-2.02bn
Raise child benefit by 25GBP/week per additional child £-2.00bn £-1.76bn £-1.64bn £-1.54bn £-1.44bn £-1.34bn £-1.24bn
Reduce Universal Credit taper rate to 20% £-20.54bn £-21.09bn £-21.45bn £-21.87bn £-21.95bn £-22.32bn £-22.79bn
Raise Class 1 main employee NICs rate to 10% £11.06bn £11.51bn £11.83bn £12.14bn £12.47bn £12.81bn £13.29bn
Raise VAT standard rate by 2pp £25.01bn £25.68bn £26.29bn £26.92bn £27.58bn £28.26bn £28.95bn
Raise additional rate by 3pp £2.83bn £3.07bn £3.27bn £3.47bn £3.67bn £3.91bn £4.23bn
Raise the Universal Credit standard allowance by 10% £-3.04bn £-3.17bn £-3.24bn £-3.32bn £-3.37bn £-3.42bn £-3.47bn
Raise the State Pension by 10% £-8.92bn £-9.13bn £-9.03bn £-9.06bn £-9.26bn £-9.51bn £-9.78bn
Standard reforms: change in each reform's target: head levels
Measure (head) 2025-26 2026-27 2027-28 2028-29 2029-30 2030-31 2031-32
Raise basic rate by 1pp: change in income_tax £6.36bn £6.65bn £6.87bn £7.07bn £7.29bn £7.53bn £7.81bn
Raise higher rate by 1pp: change in income_tax £3.55bn £3.83bn £4.06bn £4.28bn £4.50bn £4.78bn £4.97bn
Raise personal allowance by ~800GBP/year: change in income_tax £-3.96bn £-4.11bn £-4.19bn £-4.27bn £-4.36bn £-4.47bn £-1.77bn
Raise child benefit by 25GBP/week per additional child: change in child_benefit £2.34bn £2.15bn £2.03bn £1.92bn £1.82bn £1.71bn £1.59bn
Reduce Universal Credit taper rate to 20%: change in universal_credit £20.53bn £21.08bn £21.44bn £21.86bn £21.95bn £22.32bn £22.78bn
Raise Class 1 main employee NICs rate to 10%: change in national_insurance £11.33bn £11.79bn £12.13bn £12.44bn £12.78bn £13.13bn £13.62bn
Raise VAT standard rate by 2pp: change in vat £25.01bn £25.68bn £26.29bn £26.92bn £27.58bn £28.26bn £28.95bn
Raise additional rate by 3pp: change in income_tax £2.83bn £3.07bn £3.27bn £3.47bn £3.67bn £3.91bn £4.23bn
Raise the Universal Credit standard allowance by 10%: change in universal_credit £3.04bn £3.17bn £3.25bn £3.32bn £3.37bn £3.43bn £3.47bn
Raise the State Pension by 10%: change in state_pension £12.25bn £12.71bn £12.83bn £13.02bn £13.41bn £13.80bn £14.21bn

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MaxGhenis marked this pull request as ready for review October 22, 2026 19:24
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MaxGhenis added this pull request to the merge queue Oct 22, 2026
@juaristi22 juaristi22 mentioned this pull request Oct 22, 2026
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Merged via the queue into main with commit 52b3bb6 Oct 23, 2026
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MaxGhenis deleted the fix/ma-cps-trigger-2551 branch October 23, 2026 04:16
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MaxGhenis commented Oct 23, 2026

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Merged by the UK hub (Claude session 8e19f9d5) at head 38830058a, through the merge queue with the head pinned.

  • Independent review: GPT-6.1 Sol, APPROVE at 38830058a, in a combined review of four tax PRs. It confirmed that statutory Marriage Allowance changes no longer switch on the CPS-expanded Marriage Allowance reform, whose own switches still work. Local test runs were blocked by host disk; the approval rests on a source review against the law and the published statistics, and on passing CI.
  • CI: every check passes at this head. The merge queue re-runs the full suite against current main.
  • Why now: Max asked on 22 Oct to clear the UK PR backlog before the Budget.

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MaxGhenis commented Oct 23, 2026

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Confirmed on the released fix. I reran the #2551 reproduction (docs/uk_replay/evidence/policy_experiments/marriage_allowance_cps_trigger.py in PolicyEngine/policyengine-scorecard#210) on policyengine-uk 2.148.2 with core 3.33.3, in 2025, with the statutory marriage_allowance.max set to 0:

Couple 2.143.0 2.148.2
£30,000 earner (basic rate) allowance stays £1,260; income tax unchanged allowance £0; income tax +£252
£60,000 earner (higher rate) allowance becomes £1,260; income tax −£504 allowance £0; income tax unchanged

That is the expected statutory behaviour. The national rerun of the scorecard's as2013_marriage_allowance policy experiment will come with the next Microcosm cut, which is built on a fixed engine.

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@MaxGhenis MaxGhenis mentioned this pull request Oct 23, 2026
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Setting the statutory Marriage Allowance rate switches on the CPS expanded Marriage Allowance reform

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