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Compare a pull request with its merge commit's first parent in the Aggregate impact report - #2522

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Compare a pull request with its merge commit's first parent in the Aggregate impact report#2522
MaxGhenis merged 1 commit into
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fix/aggregate-impact-merge-parent

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@MaxGhenis

@MaxGhenis MaxGhenis commented Oct 20, 2026 •
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Defect

For pull_request runs, .github/workflows/aggregate-impact.yaml measured GitHub's merge commit ($GITHUB_SHA) against github.event.pull_request.base.sha. Its comment said the merge commit's first parent is the base, but pull_request.base.sha is not that parent. It lags main once main moves on. The report then counted main's newer merges as the pull request's own impact.

PR Report base Merge commit Merge commit's first parent Main commits mixed in Effect
#2516 685963c2d 207aae39f (run 39364560222) 815f89cb7 26 55 flagged moves, e.g. Universal Credit −£410m to −£464m a year, on a PR that only rewires CTR and Income Support pension-contribution rates
#2518 7e8682590 f0732e38b b9b567144 10, including #2458, #2460, #2464 and #2466 report not attributable to the PR
#2507, #2508 815f89cb7 — 815f89cb7 0 clean

(Parents from gh api repos/PolicyEngine/policyengine-uk/commits/<merge>. On the source of #2516's moves: its previous run, 39356846876, already mixed in #2457, #2458, #2460, #2464 and #2466 and flagged nothing. The 55 flags arrived with #2468, #2469, #2470, #2472 and #2475.)

Fix

  • Check out the head: fetches the merge commit with its parents (fetch-depth: 2).
  • Choose the base (new step, between the two checkouts): for a pull request, it reads the merge commit's first parent with git -C head rev-list --parents -n 1 HEAD. This is the same approach as pr_code_changes.yaml's Changes job (fetch-depth: 2, base=HEAD^1), so there is no API call and no token.
    • If the head doesn't have exactly two parents, the job fails with an error naming the commit and its parent count.
  • Check out the base: uses that SHA (steps.base.outputs.sha).
  • workflow_dispatch: unchanged. "Choose the commits" still sets its base from the input (default main), and "Choose the base" passes it through.
  • base_name: still the base ref (main). The report header already prints each side's checked-out SHA (git rev-parse HEAD in each checkout), so it now shows the first parent with no change to the tool.
  • No step reads pull_request.base.sha any more. The comments now say what the base is and why.

Invariant: for every pull_request run, base equals the merge commit's first parent, so the report is exactly what merging would change. Equivalently, no commit of the base branch is counted as the pull request's: the commits the comparison attributes (base..merge) are the pull request's own commits and the merge commit.

Tests

policyengine_uk/tests/code_health/test_aggregate_impact_workflow.py now runs the workflow's own step scripts with bash -eo pipefail. Actions runs these steps with bash -e {0}; neither script has a pipe, so the two behave the same here. They run on real git histories, with the head fetched by SHA at the depth that "Check out the head" sets.

  • test_a_pull_request_is_compared_with_its_merge_commits_first_parent: main moves on after the PR forks. The base is main's tip, and only the PR's commit and the merge are attributed. Against the fork point (what pull_request.base.sha can still name), main's two later merges were attributed too.
  • test_no_commit_of_the_base_branch_counts_as_the_pull_requests (Hypothesis, 25 derandomized examples): any mix of main commits, PR commits and "Update branch" merges. The base is always the first parent, and the attributed commits are exactly the PR's own plus the merge.
  • test_a_head_that_does_not_merge_two_commits_has_no_base[0, 1, 3]: a root commit, a plain commit and an octopus merge each fail the job with the error and set no base.
  • test_the_events_base_sha_is_not_the_comparison_base: no ${{ }} expression reads pull_request.base.sha. The steps run in order (choose the commits, check out the head, choose the base, check out the base), and the base checkout uses steps.base.outputs.sha.
  • test_a_pull_request_head_is_its_merge_commit, and test_a_dispatch_compares_the_commits_it_names for both default and given inputs: dispatch outputs are as before.
  • The data-protection tests are unchanged and pass.

Results:

  • The module passes locally: 15 tests.
  • uvx ruff format --check . passes, and ruff check on the test module is clean.
  • Against main's workflow, the reproducer fails (no step reads the first parent), and so does the expression test (it finds github.event.pull_request.base.sha).
  • Each of five mutations of the fixed workflow fails at least one test:
    • taking the second parent: 2 tests;
    • dropping fetch-depth: 2: 4;
    • dropping the parent-count check: 3;
    • reading pull_request.base.sha again: 1;
    • pointing the base checkout back at steps.commits.outputs.base: 1.

Audit of past reports

Scope: every PR merged since 2026-10-18 23:00Z (#2335 onwards), and every open PR with an aggregate-impact comment. Every version of each report comment was checked, using GitHub's edit history, with the GitHub API only.

PR Latest report Main commits mixed in Does the PR body rely on it? Status
#2518 39357512049: 0 flags, but Universal Credit +£10.1m to +£11.5m a year from #2458, #2460, #2464 and #2466 10 Yes: the status line says this report found "no change in any figure". The conclusion holds on the clean run 39336840223 the body cites in detail affected
#1913 39363356880: 4 flags 1 (version commit 815f89cb7, no model file) The table cites the clean run 39315770092. One sentence ("left the HB and CTR rows unchanged in the next run") leans on run 39357614148, which mixed in 15 commits (#2456 to #2466) affected (one sentence)
#2516 39364560222: 55 flags (Universal Credit −£393.7m to −£463.7m a year) 26 No: "no change" cites the clean run 39331419558 comment contaminated
#2189 39287947629: 41 flags (VAT −£1.20bn to −£1.97bn a year) 93 (11 merged PRs) No comment contaminated
#1661 39267217406: FAIL 100 (13 merged PRs) No comment contaminated: the base 62a0117f9a has no war_widows_pension, so the base measurement crashed. The one "broken" check (sign:vat) fails on both sides in clean reports

Every other PR with a report is clean.

Owed after this merges: a fresh run on #2518, #1913, #2516, #2189 and #1661, by a push or by merging main. Then #2518's status line and #1913's sentence can rest on clean reports. This PR edits none of them.

Impact

CI only.

  • No model, parameter or dataset file changes. Apart from the workflow, the PR changes only a test module and a changelog fragment.
  • The fixed fragment calls for a patch release (.github/bump_version.py, infer_bump).
  • This PR's own Aggregate impact run uses the fixed workflow, because a pull_request run takes the workflow file from the merge commit. Report each pull request's effect on national aggregates on the certified dataset #2335's reports show this: it posted them for a week before the workflow reached main. With no model change, this PR's report should show no change.

Reproducer: policyengine_uk/tests/code_health/test_aggregate_impact_workflow.py::test_a_pull_request_is_compared_with_its_merge_commits_first_parent

axiom: n/a: CI tooling

🤖 Generated with Claude Code

@MaxGhenis @claude
Compare a pull request's merge commit with its first parent
10ee9bc 
For pull_request runs, the Aggregate impact workflow compared GitHub's
merge commit with github.event.pull_request.base.sha. That SHA lags the
base branch once the branch moves on, so the report counted main's newer
merges as the pull request's impact (#2516's report took in 26 commits
from main, #2518's 10).

The head is now checked out with its parents (fetch-depth 2), and a new
"Choose the base" step reads the merge commit's first parent from it, as
pr_code_changes.yaml's Changes job already does. The step fails the job
if the head does not have exactly two parents. A workflow_dispatch run
passes its base through unchanged.

The tests run the workflow's own step scripts on real git histories, with
the head fetched at the workflow's fetch depth: the base is the first
parent for any history (Hypothesis), a head without two parents fails,
no step reads pull_request.base.sha, and a dispatch is unchanged.

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

MaxGhenis commented Oct 20, 2026

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Hand-off to the UK hub (build job 20261020-025958-fix-impact-base)

@MaxGhenis MaxGhenis mentioned this pull request Oct 20, 2026
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Aggregate impact on certified data: pass

Base 47642d1ee0 against head 61a8be75b6, 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.

  • incapacity_benefit: pension_credit responds only through other heads in fewer than 10 households (other heads that moved there: carers_allowance; gov_spending; not a failure)
  • incapacity_benefit: pension_credit responds only through other heads in fewer than 10 households (other heads that moved there: carers_allowance; household_benefits; not a failure)
  • maternity_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)
  • maternity_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)
  • declared double count corporate_sdlt is still contained in expected_sdlt (coefficient 1.000; Corporate SDLT is counted twice in household and government tax totals #2159)
Provenance
Side Commit Runtime Environment hash Partition hash Time
base main 47642d1ee0 uk 2.140.0 (files 6811dd0f7ec5), core 3.33.2, py 3.13.16 aarch64 5e53eba11a50 0d0426ee9e38 901.68s
head #2522 merged into main 61a8be75b6 uk 2.140.0 (files 6811dd0f7ec5), core 3.33.2, py 3.13.16 aarch64 5e53eba11a50 0d0426ee9e38 910.03s

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 £299.29bn £318.98bn £336.45bn £351.55bn £367.04bn £385.12bn £403.42bn
National Insurance (employee and self-employed) £52.58bn £54.94bn £56.75bn £58.48bn £60.51bn £62.45bn £64.90bn
National Insurance (employer) £152.64bn £159.18bn £164.14bn £168.73bn £175.57bn £181.08bn £188.22bn
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 £6.68bn £7.06bn £7.04bn £7.11bn £7.23bn £7.37bn £7.46bn
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 £83.09bn £84.89bn £86.65bn £87.58bn £89.00bn £90.33bn
Housing Benefit £8.60bn £8.93bn £9.20bn £9.34bn £9.62bn £9.88bn £10.17bn
Council Tax Reduction £1.99bn £2.03bn £2.08bn £2.13bn £2.18bn £2.24bn £2.29bn
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 1,491k 1,489k 1,477k 1,455k 1,457k 1,454k 1,451k
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 1,253k 1,254k 1,240k 1,245k 1,247k 1,249k
Council Tax Reduction 3,187k 3,213k 3,226k 3,247k 3,263k 3,282k 3,296k
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 £899.39bn £939.21bn £976.17bn £1,009.31bn £1,044.89bn £1,081.66bn £1,122.50bn
Government spending £536.61bn † £550.95bn † £557.29bn † £564.36bn † £572.91bn † £582.17bn † £591.33bn †
Government balance, each receipt once £362.78bn † £388.26bn † £418.88bn † £444.96bn † £471.97bn † £499.50bn † £531.17bn †
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 £902.52bn £942.34bn £979.30bn £1,012.44bn £1,048.02bn £1,084.79bn £1,125.63bn
household_tax £496.17bn £522.63bn £548.43bn £570.57bn £592.62bn £617.00bn £643.70bn
pre_budget_change_household_tax £488.34bn £514.51bn £540.08bn £561.53bn £583.34bn £607.46bn £633.81bn
gov_spending £536.61bn † £550.95bn † £557.29bn † £564.36bn † £572.91bn † £582.17bn † £591.33bn †
household_benefits £536.61bn † £550.95bn † £557.29bn † £564.36bn † £572.91bn † £582.17bn † £591.33bn †
gov_balance £365.91bn † £391.39bn † £422.01bn † £448.09bn † £475.10bn † £502.63bn † £534.30bn †
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 £1,887.41bn £1,945.59bn £2,017.37bn
Household net income £1,658.22bn † £1,706.81bn † £1,738.65bn † £1,772.83bn † £1,809.10bn † £1,850.82bn † £1,902.56bn †
Household net income (HBAI definition) £1,466.78bn £1,513.59bn £1,545.85bn £1,578.89bn £1,613.08bn £1,652.21bn £1,702.66bn
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% 13.5%
Absolute poverty, after housing costs: everyone 20.9% 20.4% 21.0% 21.2% 21.5% 21.7% 21.8%
Absolute poverty, after housing costs: children 31.8% 30.0% 30.7% 31.0% 31.2% 31.6% 31.8%
Absolute poverty, after housing costs: working-age adults 19.4% 19.2% 20.0% 20.2% 20.5% 20.7% 20.8%
Absolute poverty, after housing costs: pensioners 12.5% 12.2% 12.0% 12.2% 12.2% 12.3% 12.3%
Relative poverty, before housing costs: everyone 16.9% 16.4% 16.5% 16.5% 16.6% 16.7% 16.7%
Relative poverty, before housing costs: children 25.6% 23.5% 23.3% 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% 14.3% 14.3% 14.2% 14.2% 14.4%
Relative poverty, after housing costs: everyone 21.5% 21.1% 21.3% 21.3% 21.5% 21.5% 21.8%
Relative poverty, after housing costs: children 32.6% 31.3% 31.1% 31.1% 31.4% 31.3% 31.8%
Relative poverty, after housing costs: working-age adults 19.8% 19.8% 20.2% 20.3% 20.5% 20.6% 20.7%
Relative poverty, after housing costs: pensioners 13.3% 12.7% 12.6% 12.3% 12.3% 12.2% 12.3%
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 11,078k 11,209k 11,217k
Absolute poverty, before housing costs: children 3,560k 3,141k 3,261k 3,253k 3,298k 3,334k 3,334k
Absolute poverty, before housing costs: working-age adults 5,864k 5,737k 6,070k 6,165k 6,237k 6,314k 6,319k
Absolute poverty, before housing costs: pensioners 1,627k 1,549k 1,517k 1,529k 1,543k 1,560k 1,565k
Absolute poverty, after housing costs: everyone 14,540k 14,214k 14,692k 14,933k 15,150k 15,388k 15,522k
Absolute poverty, after housing costs: children 4,767k 4,515k 4,643k 4,699k 4,756k 4,835k 4,896k
Absolute poverty, after housing costs: working-age adults 8,277k 8,253k 8,666k 8,844k 8,993k 9,141k 9,203k
Absolute poverty, after housing costs: pensioners 1,496k 1,445k 1,382k 1,390k 1,402k 1,412k 1,424k
Relative poverty, before housing costs: everyone 11,759k 11,456k 11,529k 11,625k 11,706k 11,867k 11,914k
Relative poverty, before housing costs: children 3,840k 3,538k 3,515k 3,525k 3,546k 3,582k 3,602k
Relative poverty, before housing costs: working-age adults 6,154k 6,160k 6,366k 6,465k 6,537k 6,651k 6,651k
Relative poverty, before housing costs: pensioners 1,765k 1,758k 1,648k 1,634k 1,623k 1,634k 1,661k
Relative poverty, after housing costs: everyone 14,912k 14,719k 14,901k 15,009k 15,218k 15,281k 15,509k
Relative poverty, after housing costs: children 4,889k 4,715k 4,697k 4,720k 4,791k 4,799k 4,891k
Relative poverty, after housing costs: working-age adults 8,435k 8,497k 8,758k 8,884k 9,018k 9,074k 9,197k
Relative poverty, after housing costs: pensioners 1,588k 1,506k 1,446k 1,406k 1,408k 1,408k 1,422k
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 0.3052 0.3065 0.3072 0.3078 0.3084 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 † £18,017 † £18,326 † £18,522 † £18,685 †
Decile 2: mean household_net_income per household £28,364 † £29,040 † £28,680 † £29,001 † £29,377 † £29,781 † £30,332 †
Decile 3: mean household_net_income per household £34,611 † £35,900 † £36,502 † £37,005 † £37,283 † £37,961 † £38,665 †
Decile 4: mean household_net_income per household £39,326 † £40,904 † £41,932 † £42,824 † £43,176 † £43,833 † £44,936 †
Decile 5: mean household_net_income per household £44,874 † £46,154 † £46,943 † £47,447 † £48,381 † £49,255 † £50,076 †
Decile 6: mean household_net_income per household £47,930 † £49,323 † £50,259 † £51,047 † £52,157 † £52,925 † £54,240 †
Decile 7: mean household_net_income per household £56,335 † £57,591 † £58,487 † £59,458 † £60,171 † £61,648 † £62,900 †
Decile 8: mean household_net_income per household £69,228 † £70,340 † £71,615 † £72,863 † £74,332 † £75,678 † £77,547 †
Decile 9: mean household_net_income per household £79,674 † £82,009 † £83,247 † £84,449 † £86,137 † £87,749 † £89,958 †
Decile 10: mean household_net_income per household £117,666 † £120,533 † £122,448 † £124,609 † £126,968 † £129,679 † £132,877 †
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 £-4.11bn £-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 £-21.10bn £-21.45bn £-21.88bn £-21.96bn £-22.33bn £-22.81bn
Raise Class 1 main employee NICs rate to 10% £11.06bn £11.51bn £11.83bn £12.14bn £12.46bn £12.80bn £13.28bn
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 £3.26bn £3.46bn £3.66bn £3.89bn £4.21bn
Raise the Universal Credit standard allowance by 10% £-3.04bn £-3.17bn £-3.24bn £-3.32bn £-3.37bn £-3.43bn £-3.47bn
Raise the State Pension by 10% £-8.93bn £-9.14bn £-9.04bn £-9.09bn £-9.29bn £-9.54bn £-9.81bn
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 £3.54bn £3.83bn £4.06bn £4.28bn £4.50bn £4.77bn £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 £21.09bn £21.44bn £21.87bn £21.95bn £22.32bn £22.80bn
Raise Class 1 main employee NICs rate to 10%: change in national_insurance £11.33bn £11.79bn £12.13bn £12.44bn £12.77bn £13.12bn £13.61bn
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 £3.26bn £3.46bn £3.66bn £3.89bn £4.21bn
Raise the Universal Credit standard allowance by 10%: change in universal_credit £3.04bn £3.17bn £3.25bn £3.32bn £3.38bn £3.43bn £3.48bn
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 added this pull request to the merge queue Oct 20, 2026
Merged via the queue into main with commit 29e52f5 Oct 20, 2026
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MaxGhenis deleted the fix/aggregate-impact-merge-parent branch October 20, 2026 15:06
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MaxGhenis commented Oct 20, 2026

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Merged by the UK hub (session local_8e19f9d5, Opus 5.5) on its merge gates. One merge-queue enqueue, pinned to head 10ee9bcbbdff6b08cfc8605b855c37378a0f7f8c.

  • Review: GPT-6.1 Sol, APPROVE WITH NITS at 10ee9bcbb, executed (~/reviews/uk-hub/reviews/uk2522/review-full.md).
    • Its live checks:
    • Nits (non-blocking): the shell wording (the body is corrected); the parent-count message; an optional second-parent check.
    • Follow-up: pr_fix_evidence.yaml may lag in the same way. That is a separate task.
  • Impact: CI tooling only. The model is unchanged (this PR's Aggregate impact report: 0 flags against 47642d1ee). The fixed fragment cuts a patch release.
  • Checks: every check passed at the head, and the merge queue re-tested against current main.

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@vahid-ahmadi vahid-ahmadi mentioned this pull request Oct 20, 2026
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@MaxGhenis MaxGhenis mentioned this pull request Oct 20, 2026
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@juaristi22 juaristi22 mentioned this pull request Oct 20, 2026
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