Detect undeclared tax movement at any baseline level and count non-finite responses as movement by MaxGhenis · Pull Request #2758 · PolicyEngine/policyengine-uk

MaxGhenis · 2026-10-31T04:06:57Z

What and why

The aggregate checker in policyengine_uk/utils/aggregate_impact/guard.py judged movement in an undeclared tax head against a level-based allowance: £0.02 plus 2e-6 of the head's baseline. Once a household's head reached about £490,000, a £1 one-for-one response fit inside that allowance and passed.

This PR moves undeclared tax movement onto the response allowance that declared readers already use, 0.02 × |expected| + 2e-6 × |response|. Here expected counts the pounds the checker added in the household: £1 for each perturbed unit. A new predicate, _moves(response, expected, allowances=1), holds the rule in one place. The initial screen in judge_total and the first held check in still_breaks call it with one allowance. The held-slope check in breaks_on_slope passes allowances=2 at its call, because it compares two points.

_moves also counts any non-finite response as movement. The response allowance grows with the response, so an infinite response would get an infinite allowance, and NaN compares false against any allowance.

Invariants

These hold for every household, response r and addition e ≥ 0:

Exact boundaries. With finite r, the initial screen and the first held check report movement exactly when |r| > 0.02|e| + 2e-6|r|. The held slope reports it exactly when |r| exceeds twice that allowance.
No level dependence. Neither head's baseline level changes a movement verdict.
Non-finite responses move. Every path reports movement for +inf, -inf and NaN.
Sign symmetry. r and -r get the same verdict on every path.
Path agreement. The initial screen and the first held check report the same households. The held slope reports a subset of them.
Zero and unit responses. A zero response never moves. With e > 0, a one-for-one response (r = ±e) always moves.
Held checks stay in scope. A held check reports only households it receives.
Other checks unchanged. Own-head checks, declared-reader containment, spending rises and model-total checks give main's results.

Hypothesis properties in test_aggregate_impact_guard.py test invariants 1 to 7 over levels from £0 to £1bn, additions from £0 to £1m and responses up to £1tn. One of them tests invariant 5 as a differential between the two implementations of the first-point rule, the screen in judge_total and still_breaks. A table test pins each side of each boundary. It includes expected = 1, response = 0.03, which the initial and first held checks reject and the held slope accepts. Two tests run the complete guard on a small hand-built model. One runs a £1 containment at levels of £0, £490,000 and £1bn; the other runs infinite, negative-infinite and NaN responses.

Compatibility

A counted_once:<component> check that passes on main can now fail. That happens when an undeclared tax head's response exceeds the response allowance, fits within main's level allowance, and still moves with the other heads held. This covers containment, partial responses and negative responses.
A check that fails on main can now pass, because the allowance now grows with the pounds added, as the issue asks. With £2 added, a £0.03 response and a zero baseline, main fails and this branch passes.
In a household where the checker added nothing, any non-zero response now counts as movement. Main allowed £0.02 plus the level term there.
NaN changes from main. Main lets a NaN response pass all three movement checks, because nan > x is false; this branch fails it. Main already fails +inf and -inf, and so does this branch.
Two NaN heads. When two undeclared heads both turn NaN, main reports a pass and this branch stops with Core's ValueError, raised as it sets the held heads as inputs. #2759 covers that error and the four other checks that still pass NaN.
Independent heads with zero response still pass.
A limit this branch shares with main. Core stores float variables as float32, which can't hold a £1 change at a level of £16,777,216 or above. Both guards pass such a change. The complete-guard test at £1bn uses a float64 fake model, so it doesn't cover that storage.

My local runs used no survey data. The aggregate report runs one guard on both sides, so the test plan compares it with reports from main's guard.

No file overlaps with #2719 or with open #2700, #2727 and #2735; #2731 and #2234 have merged. The branch merges cleanly into main at 03349c9d5, and its diff applies cleanly onto #2719's head (c086c4917). With this diff on each, the guard file passes 63 of 63 and the partition subset below passes 4. The branch changes no existing test's expected value.

Test plan

For policy changes: not applicable. The change touches checker tooling only, and no parameter, variable or policy test.
Ruff 0.17.2: ruff format --check and ruff check pass on both changed Python files. ruff check --select F811,F821 policyengine_uk passes across 1,895 Python files, and git diff --check passes.
Changelog fragment changelog.d/2606.fixed.md.
Aggregate report: the counted-once check fails none of its 91 components in 2026-27, on the same certified dataset (sha256 056e80fd8e91) where the reports on Derive economic assumption index horizon from the growth series #2756 and Correct programme agencies and national coverage #2757, which ran main's guard, fail none. The two groups of reports list the same mediated responses, so no check changes status. The check covers 2026-27 only, on main as here.

No run used survey data: I unset HUGGING_FACE_TOKEN and POLICYENGINE_UK_DEFAULT_DATASET for each one.

policyengine_uk/tests/aggregate_impact/, file by file: 330 passed, 9 skipped. test_aggregate_impact_certified.py skips all 9 of its tests because they need the survey dataset. The other counts: childcare_provenance 42, compare 133, data_mode 4, dataset 13, guard 63, measure 44, partition 11, reforms 20.
test_aggregate_impact_guard.py alone: 63 passed.
policyengine_uk/tests/code_health/test_aggregate_impact_workflow.py: 17 passed.
policyengine_uk/tests/test_fiscal_partition.py -k 'no_head_reaches_another_head_of_its_total_undeclared or declared_reads_occur': 4 passed, 39 deselected.
Against main's guard, the new tests fail 16 and pass 47. Hypothesis shrinks the failures to a one-for-one response of £0.015625 at a zero level, £0.03125 for the held slope, and a NaN response with nothing added.
Differential against main's guard on cases whose verdict this PR leaves unchanged: 1,045 comparisons match main. They cover 400 judge_total calls across spending, declared-reader, own-head and model-total cases, 600 held-check calls for containment and rises, and 45 complete-guard runs. Run directly, both guards fail +inf and -inf. NaN passes on main and fails here.

Mutation testing. I applied each mutant to a copy of the final guard and ran the final test file against it. The tests kill all 15.

Mutant	Failing tests (of 63)
Raise all three movement allowances by 50%	6
Drop the held slope's doubled allowance	5
Drop the non-finite rule	5
Count only infinite responses, so NaN passes	3
Count only NaN, so infinite responses pass	4
Compare with `>=` in place of `>`	2
Drop the response-proportional term	1
Compare the signed response in place of its magnitude	10
Triple the held slope's allowance	3
Double the allowance of the initial and first held checks	5
Restore main's level allowance in the initial screen	16
Restore it in the first held check	13
Restore it in the held slope	9
Drop `where` from the first held check	1
Drop `where` from the held slope	1

Reproducer

Reproducer: policyengine_uk/tests/aggregate_impact/test_aggregate_impact_guard.py::test_undeclared_tax_containment_fails_at_any_baseline; policyengine_uk/tests/aggregate_impact/test_aggregate_impact_guard.py::test_a_non_finite_undeclared_tax_response_fails

axiom: n/a: aggregate checker tooling, with no policy change

🤖 Generated with Claude Code

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

The response allowance grows with the response, so an infinite response got an infinite allowance and passed all three movement checks, and NaN compared false with any allowance. One predicate, _moves, now applies the rule in the initial screen and both held checks, with the held slope's doubled allowance passed at its call. Tests pin the 2% and 4% boundaries on each side, any non-finite response failing every path, and agreement between the paths. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Explicit Hypothesis examples and two table rows make the boundary tests fail deterministically when the comparison becomes non-strict or drops the response-proportional term. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

github-actions · 2026-10-31T05:14:15Z

Aggregate impact on certified data: pass

Base 03349c9d5d against head d6d9c03135, 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

Standard reform costings (change in gov_balance)

Measure	2025-26	2026-27	2027-28	2028-29	2029-30	2030-31	2031-32
Raise additional rate by 3pp	0	0	0	0	0	suppressed	suppressed

Standard reforms: change in each reform's target

Measure	2025-26	2026-27	2027-28	2028-29	2029-30	2030-31	2031-32
Raise additional rate by 3pp: change in income_tax	0	0	0	0	0	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; household income totals; population; poverty rates; people in poverty; inequality; mean household net income in each side's own deciles.

Checks failing on both base and head (1)

VAT excluding private school fees is never negative (sign:vat): 2025-26: 76 units below zero, a weighted £-53,888,684 in total; 2026-27: 76 units below zero, a weighted £-55,774,885 in total; 2027-28: 76 units below zero, a weighted £-57,687,092 in total

Counted-once check

Each of 91 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.

widowed_parents_allowance: pension_credit responds only through other heads in fewer than 10 households (other heads that moved there: carers_allowance; gov_spending; not a failure)
widowed_parents_allowance: pension_credit responds only through other heads in fewer than 10 households (other heads that moved there: carers_allowance; household_benefits; not a failure)

Provenance

Side	Commit	Runtime	Environment hash	Partition hash	Time
base	main `03349c9d5d`	uk 2.167.0 (files `3e0964c9aaed`), core 3.33.12, py 3.13.18 aarch64	`ac527ff90c6e`	`e90ddaeead60`	1976.36s
head	#2758 merged into main `d6d9c03135`	uk 2.167.0 (files `a33bb4f362ea`), core 3.33.12, py 3.13.18 aarch64	`ac527ff90c6e`	`e90ddaeead60`	1991.82s

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
Final charge on cash interest in non-cash ISAs	£0.00bn	£0.00bn	£0.00bn	£0.00bn	£0.00bn	£0.00bn	£0.00bn
Lifetime ISA withdrawal charge	£0.00bn	£0.00bn	£0.00bn	£0.00bn	£0.00bn	£0.00bn	£0.00bn
Income tax	£294.46bn	£315.23bn	£334.00bn	£349.45bn	£365.10bn	£383.16bn	£397.71bn
National Insurance (employee and self-employed)	£51.70bn	£54.14bn	£56.13bn	£57.73bn	£59.76bn	£61.64bn	£63.51bn
National Insurance (employer)	£148.71bn	£155.37bn	£160.88bn	£165.09bn	£172.06bn	£177.36bn	£182.57bn
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	£12.60bn	£13.15bn	£13.60bn	£14.11bn	£14.67bn	£15.24bn	£15.80bn
Student loan repayments	£7.82bn	£8.13bn	£8.39bn	£8.58bn	£8.79bn	£9.04bn	£9.29bn
VAT excluding private school fees	£249.37bn	£256.88bn	£266.66bn	£272.70bn	£278.97bn	£285.24bn	£291.59bn
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	£1.95bn	£2.01bn	£2.09bn	£2.14bn	£2.21bn	£2.27bn	£2.31bn
Change in private school VAT from its baseline	£0.00bn	£0.00bn	£0.00bn	£0.00bn	£0.00bn	£0.00bn	£0.00bn
Fuel duties	£24.71bn	£24.59bn	£26.54bn	£26.58bn	£26.26bn	£25.53bn	£24.40bn
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
Betting and gaming duties	£0.00bn	£0.00bn	£0.00bn	£0.00bn	£0.00bn	£0.00bn	£0.00bn
TV licence fee	£4.26bn	£4.40bn	£4.41bn	£4.42bn	£4.43bn	£4.44bn	£4.45bn
Council tax	£49.21bn	£52.16bn	£54.89bn	£57.95bn	£61.16bn	£64.47bn	£67.91bn
High value council tax surcharge	£0.00bn	£0.00bn	£0.00bn	£0.48bn	£0.49bn	£0.50bn	£0.51bn
Northern Ireland domestic rates	£0.55bn	£0.58bn	£0.60bn	£0.63bn	£0.66bn	£0.69bn	£0.72bn
Business rates	£34.68bn	£36.20bn	£38.00bn	£39.46bn	£42.27bn	£43.25bn	£44.29bn
Stamp duty land tax on the household's own purchases	£6.88bn	£7.32bn	£7.66bn	£8.06bn	£8.47bn	£8.91bn	£9.35bn
Stamp duty land tax paid by companies	£4.72bn	£4.57bn	£5.29bn	£6.03bn	£6.37bn	£6.92bn	£7.45bn
Land transaction tax (Wales)	£0.07bn	£0.08bn	£0.08bn	£0.09bn	£0.10bn	£0.10bn	£0.11bn
Land and buildings transaction tax (Scotland)	£0.31bn	£0.32bn	£0.33bn	£0.35bn	£0.36bn	£0.38bn	£0.40bn
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
Lifetime ISA bonus	£0.00bn	£0.00bn	£0.00bn	£0.00bn	£0.00bn	£0.00bn	£0.00bn
State Pension	£121.68bn	£125.92bn	£126.73bn	£129.50bn	£132.99bn	£136.66bn	£140.43bn
Pension Credit	£6.66bn	£7.03bn	£7.30bn	£7.51bn	£7.65bn	£7.84bn	£8.03bn
Winter Fuel Payment	£1.86bn	£1.85bn	£1.79bn	£1.77bn	£1.78bn	£1.78bn	£1.78bn
Pension Age Winter Heating Payment (Scotland)	£0.19bn	£0.20bn	£0.20bn	£0.21bn	£0.21bn	£0.22bn	£0.22bn
Universal Credit	£75.48bn	£80.52bn	£83.04bn	£85.11bn	£86.31bn	£87.90bn	£88.58bn
Housing Benefit	£8.56bn	£8.89bn	£9.24bn	£9.48bn	£9.72bn	£9.99bn	£10.27bn
Council Tax Reduction	£2.07bn	£2.20bn	£2.31bn	£2.45bn	£2.58bn	£2.72bn	£2.86bn
Employment and Support Allowance (income-related)	£0.79bn	£0.82bn	£0.84bn	£0.86bn	£0.88bn	£0.90bn	£0.92bn
Employment and Support Allowance (contribution-based)	£5.20bn	£5.37bn	£5.56bn	£5.69bn	£5.82bn	£5.95bn	£6.09bn
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	£0.31bn	£0.31bn	£0.32bn	£0.33bn	£0.34bn
Income Support	£0.11bn	£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	£26.95bn	£28.03bn	£29.05bn	£30.09bn	£30.75bn	£31.51bn	£32.21bn
Disability Living Allowance	£7.49bn	£7.79bn	£8.07bn	£8.36bn	£8.55bn	£8.76bn	£8.95bn
Attendance Allowance	£8.68bn	£9.03bn	£9.36bn	£9.69bn	£9.90bn	£10.15bn	£10.38bn
Carer's Allowance	£4.48bn	£4.66bn	£4.83bn	£5.00bn	£5.11bn	£5.23bn	£5.35bn
Carer Support Payment (Scotland)	£0.31bn	£0.32bn	£0.33bn	£0.34bn	£0.35bn	£0.36bn	£0.37bn
Carer's Allowance Supplement (Scotland)	£0.00bn	£0.04bn	£0.04bn	£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	£0.50bn	£0.52bn	£0.54bn	£0.55bn	£0.56bn	£0.58bn	£0.59bn
Armed Forces Compensation Scheme	£0.61bn	£0.63bn	£0.65bn	£0.66bn	£0.68bn	£0.69bn	£0.71bn
War Widow's or Widower's Pension	£0.00bn	£0.00bn	£0.00bn	£0.00bn	£0.00bn	£0.00bn	£0.00bn
Child Benefit	£16.19bn	£16.82bn	£17.39bn	£18.00bn	£18.39bn	£18.84bn	£19.25bn
Scottish Child Payment	£0.49bn	£0.52bn	£0.53bn	£0.56bn	£0.57bn	£0.57bn	£0.57bn
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	£3.30bn	£3.41bn	£3.54bn	£3.62bn	£3.70bn	£3.78bn	£3.87bn
Statutory Paternity Pay	£0.00bn	£0.00bn	£0.00bn	£0.00bn	£0.00bn	£0.00bn	£0.00bn
Statutory Sick Pay	£1.12bn	£1.16bn	£1.20bn	£1.23bn	£1.26bn	£1.29bn	£1.32bn
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	£0.71bn	£0.73bn	£0.75bn	£0.76bn	£0.78bn
Widowed Parent's Allowance	£0.00bn	£0.00bn	£0.00bn	£0.00bn	£0.00bn	£0.00bn	£0.00bn
Tax-Free Childcare	£0.56bn	£0.57bn	£0.58bn	£0.59bn	£0.61bn	£0.62bn	£0.59bn
Extended childcare entitlement	£2.99bn	£3.50bn	£3.62bn	£3.75bn	£3.83bn	£3.92bn	£4.01bn
Universal childcare entitlement	£2.06bn	£2.22bn	£2.29bn	£2.38bn	£2.44bn	£2.51bn	£2.56bn
Targeted childcare entitlement	£0.50bn	£0.51bn	£0.52bn	£0.54bn	£0.55bn	£0.57bn	£0.56bn
Childcare Offer for Wales	£0.26bn	£0.28bn	£0.28bn	£0.29bn	£0.30bn	£0.31bn	£0.32bn
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	£203.89bn	£204.30bn	£204.56bn	£204.91bn	£205.34bn	£205.85bn	£206.35bn
State education spending	£0.02bn	£0.02bn	£0.02bn	£0.02bn	£0.02bn	£0.02bn	£0.02bn
Transport subsidy spending	£25.05bn	£25.10bn	£25.14bn	£25.18bn	£25.23bn	£25.30bn	£25.36bn
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
Lifetime ISA bonus	0k	0k	0k	0k	0k	0k	0k
State Pension	11,264k	11,145k	10,819k	10,700k	10,723k	10,750k	10,776k
Pension Credit	1,486k	1,480k	1,474k	1,455k	1,453k	1,455k	1,464k
Winter Fuel Payment	7,844k	7,783k	7,473k	7,375k	7,391k	7,409k	7,427k
Pension Age Winter Heating Payment (Scotland)	803k	802k	800k	797k	799k	801k	802k
Universal Credit	6,342k	6,347k	6,350k	6,316k	6,298k	6,291k	6,246k
Housing Benefit	1,249k	1,245k	1,246k	1,229k	1,229k	1,229k	1,232k
Council Tax Reduction	3,176k	3,195k	3,200k	3,215k	3,224k	3,235k	3,242k
Employment and Support Allowance (income-related)	71k	71k	71k	71k	71k	71k	71k
Employment and Support Allowance (contribution-based)	719k	720k	721k	722k	724k	726k	728k
Jobseeker's Allowance (income-based)	0k	0k	0k	0k	0k	0k	0k
Jobseeker's Allowance (contribution-based)	67k	67k	67k	67k	67k	68k	68k
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	3,567k	3,575k	3,579k	3,585k	3,593k	3,602k	3,611k
Disability Living Allowance	1,291k	1,294k	1,296k	1,298k	1,300k	1,304k	1,307k
Attendance Allowance	1,695k	1,698k	1,700k	1,703k	1,707k	1,711k	1,715k
Carer's Allowance	1,034k	1,037k	1,038k	1,040k	1,042k	1,044k	1,046k
Carer Support Payment (Scotland)	71k	71k	71k	72k	72k	72k	72k
Carer's Allowance Supplement (Scotland)	0k	71k	71k	72k	72k	72k	72k
Severe Disablement Allowance	4k	4k	4k	4k	4k	4k	4k
Industrial Injuries Disablement Benefit	137k	137k	137k	138k	138k	138k	139k
Armed Forces Compensation Scheme	93k	93k	94k	94k	94k	94k	94k
War Widow's or Widower's Pension	0k	0k	0k	0k	0k	0k	0k
Child Benefit	8,123k	8,120k	8,120k	8,130k	8,145k	8,161k	8,178k
Scottish Child Payment	351k	352k	352k	355k	353k	351k	340k
Two Child Limit Payment (Scotland, counterfactual)	0k	0k	0k	0k	0k	0k	0k
Healthy Start vouchers	200k	200k	200k	201k	201k	201k	202k
Maternity Allowance	0k	0k	0k	0k	0k	0k	0k
Statutory Maternity Pay	333k	333k	334k	334k	335k	336k	337k
Statutory Paternity Pay	0k	0k	0k	0k	0k	0k	0k
Statutory Sick Pay	181k	182k	182k	182k	182k	183k	183k
Sure Start Maternity Grant	26k	26k	26k	26k	26k	26k	26k
Bereavement Support Payment	98k	98k	98k	98k	98k	99k	99k
Widowed Parent's Allowance	0k	0k	0k	0k	0k	0k	0k
Tax-Free Childcare	1,043k	1,027k	1,021k	1,024k	1,029k	1,026k	1,011k
Extended childcare entitlement	795k	800k	804k	806k	809k	814k	814k
Universal childcare entitlement	1,071k	1,072k	1,074k	1,076k	1,079k	1,089k	1,090k
Targeted childcare entitlement	165k	156k	154k	154k	155k	155k	150k
Childcare Offer for Wales	39k	39k	39k	39k	39k	39k	39k
Care to Learn	0k	0k	0k	0k	0k	0k	0k
Childcare Grant	0k	0k	0k	0k	0k	0k	0k
Parents' Learning Allowance	98k	98k	98k	99k	99k	99k	99k
Adult Dependants' Grant	18k	18k	12k	12k	12k	12k	12k
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	£892.00bn	£935.14bn	£979.55bn	£1,013.85bn	£1,052.14bn	£1,089.13bn	£1,122.37bn
Government spending	£529.38bn †	£543.55bn †	£550.93bn †	£559.77bn †	£567.54bn †	£576.30bn †	£584.05bn †
Government balance, each receipt once	£362.62bn †	£391.59bn †	£428.62bn †	£454.08bn †	£484.59bn †	£512.83bn †	£538.32bn †
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	£892.00bn	£935.14bn	£979.55bn	£1,013.85bn	£1,052.14bn	£1,089.13bn	£1,122.37bn
household_tax	£491.97bn	£520.87bn	£549.93bn	£573.92bn	£598.90bn	£624.26bn	£645.90bn
pre_budget_change_household_tax	£484.15bn	£512.74bn	£541.54bn	£564.86bn	£589.61bn	£614.72bn	£636.09bn
gov_spending	£529.38bn †	£543.55bn †	£550.93bn †	£559.77bn †	£567.54bn †	£576.30bn †	£584.05bn †
household_benefits	£529.38bn †	£543.55bn †	£550.93bn †	£559.77bn †	£567.54bn †	£576.30bn †	£584.05bn †
gov_balance	£362.62bn †	£391.59bn †	£428.62bn †	£454.08bn †	£484.59bn †	£512.83bn †	£538.32bn †

Household income totals: head levels

Measure (head)	2025-26	2026-27	2027-28	2028-29	2029-30	2030-31	2031-32
Household market income	£1,637.96bn	£1,702.77bn	£1,757.35bn	£1,806.41bn	£1,855.97bn	£1,912.43bn	£1,970.44bn
Household net income	£1,636.69bn †	£1,685.25bn †	£1,716.89bn †	£1,749.83bn †	£1,781.14bn †	£1,819.80bn †	£1,862.66bn †
Household net income (HBAI definition)	£1,449.57bn	£1,497.73bn	£1,532.81bn	£1,567.22bn	£1,600.03bn	£1,638.06bn	£1,679.23bn

Population: head levels

Measure (head)	2025-26	2026-27	2027-28	2028-29	2029-30	2030-31	2031-32
People	69,245k	69,383k	69,473k	69,592k	69,738k	69,912k	70,080k
Benefit units	35,110k	35,181k	35,226k	35,286k	35,360k	35,449k	35,534k
Households	31,046k	31,108k	31,149k	31,201k	31,267k	31,345k	31,420k

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	16.3%	15.6%	16.4%	16.3%	16.5%	16.5%	16.6%
Absolute poverty, before housing costs: children	24.7%	22.3%	23.3%	22.9%	23.1%	23.2%	23.4%
Absolute poverty, before housing costs: working-age adults	14.1%	13.9%	14.7%	14.7%	14.8%	14.8%	14.9%
Absolute poverty, before housing costs: pensioners	13.7%	13.5%	14.0%	13.9%	14.0%	13.9%	13.9%
Absolute poverty, after housing costs: everyone	21.6%	21.1%	22.0%	22.5%	22.7%	23.0%	23.3%
Absolute poverty, after housing costs: children	33.3%	31.3%	32.2%	32.4%	32.5%	33.0%	33.9%
Absolute poverty, after housing costs: working-age adults	19.9%	19.9%	20.8%	21.5%	21.8%	22.0%	22.2%
Absolute poverty, after housing costs: pensioners	12.7%	12.6%	13.1%	13.2%	13.3%	13.4%	13.5%
Relative poverty, before housing costs: everyone	17.0%	16.3%	16.4%	16.3%	16.3%	16.3%	16.7%
Relative poverty, before housing costs: children	25.9%	23.4%	23.3%	22.9%	22.8%	22.9%	23.7%
Relative poverty, before housing costs: working-age adults	14.5%	14.3%	14.6%	14.7%	14.7%	14.7%	15.0%
Relative poverty, before housing costs: pensioners	14.5%	14.7%	13.9%	13.9%	13.8%	13.9%	14.0%
Relative poverty, after housing costs: everyone	21.4%	21.0%	21.2%	21.3%	21.3%	21.5%	21.7%
Relative poverty, after housing costs: children	33.1%	31.1%	31.1%	31.0%	31.1%	31.2%	31.7%
Relative poverty, after housing costs: working-age adults	19.9%	19.8%	20.2%	20.4%	20.5%	20.6%	20.8%
Relative poverty, after housing costs: pensioners	12.5%	12.4%	12.2%	11.7%	11.7%	11.8%	12.0%

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	11,278k	10,837k	11,403k	11,358k	11,478k	11,506k	11,643k
Absolute poverty, before housing costs: children	3,688k	3,332k	3,496k	3,437k	3,477k	3,499k	3,545k
Absolute poverty, before housing costs: working-age adults	5,965k	5,921k	6,308k	6,354k	6,417k	6,426k	6,517k
Absolute poverty, before housing costs: pensioners	1,624k	1,584k	1,599k	1,568k	1,583k	1,580k	1,581k
Absolute poverty, after housing costs: everyone	14,944k	14,662k	15,296k	15,679k	15,862k	16,047k	16,331k
Absolute poverty, after housing costs: children	4,975k	4,689k	4,832k	4,863k	4,898k	4,986k	5,125k
Absolute poverty, after housing costs: working-age adults	8,463k	8,491k	8,965k	9,325k	9,464k	9,549k	9,669k
Absolute poverty, after housing costs: pensioners	1,506k	1,482k	1,500k	1,491k	1,500k	1,513k	1,537k
Relative poverty, before housing costs: everyone	11,750k	11,332k	11,389k	11,348k	11,358k	11,410k	11,702k
Relative poverty, before housing costs: children	3,872k	3,504k	3,496k	3,434k	3,431k	3,451k	3,577k
Relative poverty, before housing costs: working-age adults	6,159k	6,103k	6,301k	6,349k	6,363k	6,388k	6,540k
Relative poverty, before housing costs: pensioners	1,720k	1,724k	1,592k	1,565k	1,563k	1,571k	1,585k
Relative poverty, after housing costs: everyone	14,849k	14,583k	14,728k	14,809k	14,885k	15,005k	15,219k
Relative poverty, after housing costs: children	4,942k	4,664k	4,660k	4,663k	4,681k	4,702k	4,798k
Relative poverty, after housing costs: working-age adults	8,426k	8,460k	8,679k	8,821k	8,877k	8,964k	9,056k
Relative poverty, after housing costs: pensioners	1,482k	1,459k	1,389k	1,325k	1,327k	1,340k	1,366k

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	0.3080	0.3057	0.3063	0.3062	0.3068	0.3073	0.3089

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	£17,681 †	£17,895 †	£17,904 †	£18,146 †	£18,308 †	£18,581 †	£18,739 †
Decile 2: mean household_net_income per household	£27,939 †	£28,874 †	£28,683 †	£29,083 †	£29,354 †	£29,679 †	£30,165 †
Decile 3: mean household_net_income per household	£34,320 †	£35,455 †	£36,108 †	£36,626 †	£37,218 †	£37,722 †	£38,220 †
Decile 4: mean household_net_income per household	£38,933 †	£40,603 †	£41,873 †	£42,783 †	£43,423 †	£43,928 †	£44,548 †
Decile 5: mean household_net_income per household	£43,239 †	£45,442 †	£45,787 †	£46,995 †	£47,729 †	£48,921 †	£50,229 †
Decile 6: mean household_net_income per household	£47,927 †	£49,126 †	£50,887 †	£51,728 †	£52,601 †	£54,202 †	£55,188 †
Decile 7: mean household_net_income per household	£55,662 †	£56,509 †	£57,442 †	£57,965 †	£59,083 †	£59,211 †	£60,675 †
Decile 8: mean household_net_income per household	£68,789 †	£70,704 †	£71,779 †	£73,356 †	£73,952 †	£75,362 †	£77,248 †
Decile 9: mean household_net_income per household	£78,890 †	£80,992 †	£82,907 †	£84,246 †	£85,584 †	£87,169 †	£89,597 †
Decile 10: mean household_net_income per household	£117,005 †	£120,262 †	£122,221 †	£124,681 †	£126,775 †	£129,108 †	£131,486 †

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	£6.41bn	£6.66bn	£6.64bn	£6.86bn	£7.04bn	£7.26bn	£7.48bn
Raise higher rate by 1pp	£3.61bn	£3.87bn	£4.00bn	£4.21bn	£4.43bn	£4.71bn	£4.83bn
Raise personal allowance by ~800GBP/year	£-3.80bn	£-3.92bn	£-3.98bn	£-4.09bn	£-4.17bn	£-4.21bn	£-1.94bn
Raise child benefit by 25GBP/week per additional child	£-1.99bn	£-1.75bn	£-1.55bn	£-1.39bn	£-1.30bn	£-1.17bn	£-1.06bn
Reduce Universal Credit taper rate to 20%	£-20.77bn	£-21.32bn	£-21.78bn	£-22.02bn	£-22.36bn	£-22.77bn	£-22.96bn
Raise Class 1 main employee NICs rate to 10%	£10.89bn	£11.30bn	£11.71bn	£12.01bn	£12.31bn	£12.62bn	£13.01bn
Raise VAT standard rate by 2pp	£24.89bn	£25.71bn	£26.63bn	£27.24bn	£27.87bn	£28.50bn	£29.14bn
Raise additional rate by 3pp	£2.90bn	£3.15bn	£3.22bn	£3.42bn	£3.61bn	suppressed	suppressed
Raise the Universal Credit standard allowance by 10%	£-3.06bn	£-3.18bn	£-3.27bn	£-3.35bn	£-3.44bn	£-3.48bn	£-3.50bn
Raise the State Pension by 10%	£-7.78bn	£-8.01bn	£-7.99bn	£-8.14bn	£-8.42bn	£-8.55bn	£-8.89bn

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	£6.55bn	£6.86bn	£6.80bn	£7.01bn	£7.21bn	£7.44bn	£7.66bn
Raise higher rate by 1pp: change in income_tax	£3.61bn	£3.92bn	£4.01bn	£4.23bn	£4.45bn	£4.72bn	£4.84bn
Raise personal allowance by ~800GBP/year: change in income_tax	£-3.93bn	£-4.07bn	£-4.16bn	£-4.25bn	£-4.32bn	£-4.38bn	£-1.75bn
Raise child benefit by 25GBP/week per additional child: change in child_benefit	£2.33bn	£2.14bn	£1.94bn	£1.76bn	£1.65bn	£1.52bn	£1.40bn
Reduce Universal Credit taper rate to 20%: change in universal_credit	£20.74bn	£21.31bn	£21.77bn	£22.02bn	£22.34bn	£22.74bn	£22.96bn
Raise Class 1 main employee NICs rate to 10%: change in national_insurance	£11.15bn	£11.63bn	£12.00bn	£12.29bn	£12.61bn	£12.94bn	£13.31bn
Raise VAT standard rate by 2pp: change in vat	£24.69bn	£25.51bn	£26.42bn	£27.03bn	£27.65bn	£28.28bn	£28.91bn
Raise additional rate by 3pp: change in income_tax	£2.90bn	£3.15bn	£3.22bn	£3.42bn	£3.62bn	suppressed	suppressed
Raise the Universal Credit standard allowance by 10%: change in universal_credit	£3.06bn	£3.19bn	£3.29bn	£3.37bn	£3.44bn	£3.50bn	£3.53bn
Raise the State Pension by 10%: change in state_pension	£10.68bn	£11.17bn	£11.28bn	£11.60bn	£12.04bn	£12.47bn	£12.97bn

MaxGhenis and others added 4 commits October 30, 2026 19:15

Detect undeclared tax movement independently of baseline levels

a8a582c

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Pin the held checks to the households they receive

a122f23

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

MaxGhenis mentioned this pull request Oct 31, 2026

Fail the aggregate checker's remaining checks on a NaN response #2759

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MaxGhenis marked this pull request as ready for review October 31, 2026 06:08

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Detect undeclared tax movement at any baseline level and count non-finite responses as movement - #2758

Detect undeclared tax movement at any baseline level and count non-finite responses as movement#2758
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fix-2606-undeclared-head-slack

MaxGhenis commented Oct 31, 2026 •

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Aggregate impact on certified data: pass

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MaxGhenis commented Oct 31, 2026 •

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