# Two-child limit: from the September estimate to the October one

Generated by `pipeline/decompose_uk_two_child_limit_poverty.py` from the
runs in this folder; edit the script, not this file.

Quantity: children lifted from relative poverty: with-limit world minus current law, 2029-30 (engine period 2029).

## AHC

| Step | Children lifted | Change |
|---|---:|---:|
| published September run (policyengine 5.0.2 managed route; Populace, 2.89.2, under-18s, fixed line) | 253k |  |
| 1 route: the same pair through a bare Microsimulation | 253k | +0k |
| 2 engine 2.89.2 -> 2.132.6 (Populace) | 338k | +86k |
| 3 data Populace -> Microcosm (2.132.6) | 441k | +103k |
| 4 children: under-18s -> HBAI dependent children | 448k | +6k |
| 5 line: fixed -> each world's own median (= the certified pair) | 445k | -3k |
| 6 engine 2.132.6 -> 2.148.3 (Microcosm; the docs page's run) | 548k | +102k |

Total change: +295k.

Engine and data in the other order (fixed line, under-18s):

- data first: Populace -> Microcosm on 2.89.2: +257k
- then engine 2.89.2 -> 2.132.6 on Microcosm: -68k

## BHC

| Step | Children lifted | Change |
|---|---:|---:|
| published September run (policyengine 5.0.2 managed route; Populace, 2.89.2, under-18s, fixed line) | 276k |  |
| 1 route: the same pair through a bare Microsimulation | 276k | +0k |
| 2 engine 2.89.2 -> 2.132.6 (Populace) | 306k | +30k |
| 3 data Populace -> Microcosm (2.132.6) | 449k | +143k |
| 4 children: under-18s -> HBAI dependent children | 453k | +4k |
| 5 line: fixed -> each world's own median (= the certified pair) | 450k | -3k |
| 6 engine 2.132.6 -> 2.148.3 (Microcosm; the docs page's run) | 460k | +10k |

Total change: +184k.

Engine and data in the other order (fixed line, under-18s):

- data first: Populace -> Microcosm on 2.89.2: +148k
- then engine 2.89.2 -> 2.132.6 on Microcosm: +25k

## Step 6 by release (Microcosm, HBAI dependent children, own median)

Each policyengine-uk release the bisection ran, on policyengine-core 3.33.3; only releases that move either count are listed. The last column summarises the release's section of policyengine-uk's CHANGELOG.md. A release can carry several changes; the bisection does not split one.

| Release | From | AHC | Change | BHC | Change | Releases between not run | Changelog |
|---|---|---:|---:|---:|---:|---|---|
| 2.134.5 | 2.134.4 | 445.1k | +0.0k | 443.9k | -5.7k | none | Pension contributions relief limited by relevant UK earnings; the annual allowance charge recalculated across bands. |
| 2.134.6 | 2.134.5 | 458.7k | +13.6k | 447.9k | +4.0k | none | The Universal Credit Act 2025 standard allowance uplifts for 2027-28 to 2029-30 applied through their own uprating index. |
| 2.134.8 | 2.134.7 | 450.4k | -8.2k | 447.7k | -0.1k | none | Relieved pension contributions deducted from adjusted net income (Personal Allowance taper, High Income Child Benefit Charge). |
| 2.139.2 | 2.139.1 | 455.8k | +5.3k | 447.8k | +0.1k | none | Five fixes, among them group inputs assigned to the right benefit unit and household when dataset tables are not sorted by identifier, the savings starting-rate band and Scottish thresholds. |
| 2.139.5 | 2.139.4 | 445.7k | -10.1k | 455.5k | +7.7k | none | Universal Credit's higher disabled child addition separated from tax credits; Working Tax Credit conditions on one claimant; the Child Tax Credit family element limited to children born before 6 April 2017; Child Benefit out of pensioner Council Tax Reduction income. |
| 2.141.6 | 2.141.5 | 440.9k | -4.8k | 432.8k | -22.7k | none | Fifteen input columns that declared an uprating index but stayed flat through 2030 now uprate (water and sewerage, housing service charges, salary-sacrifice pensions and others). |
| 2.145.1 | 2.145.0 | 435.4k | -5.5k | 432.6k | -0.2k | none | Additional State Pension and protected payments uprated by September CPI, not the full rate's triple-lock rise. |
| 2.146.3 | 2.146.2 | 473.6k | +38.2k | 463.4k | +30.7k | none | Universal Credit's LCWRA element, carer element and work allowance given on the claimants' own circumstances, not a dependant's. |
| 2.147.1 | 2.147.0 | 589.2k | +115.6k | 438.6k | -24.8k | none | HBAI income counts property income after finance costs (property_income_after_finance_costs), not the profit before them. |
| 2.148.2 | 2.148.1 | 547.5k | -41.7k | 460.0k | +21.4k | none | Benefits uprated by the previous September's CPI (#2533), with fixes to current_education's order dependence, the free TV licence and the Marriage Allowance reform switch. |

policyengine-core 3.33.3 to 3.33.12 at policyengine-uk 2.148.3: AHC +0k, BHC +0k.

## Every cell (fixed line / own median; under-18s, HBAI dependent children)

| Cell | AHC fixed, u18 | AHC own, u18 | AHC fixed, HBAI | AHC own, HBAI | Exchequer cost | Children without a child element (with limit) |
|---|---:|---:|---:|---:|---:|---:|
| microcosm_uk2.132.6 | 441k | 439k | 448k | 445k | £3.19bn | 911k |
| microcosm_uk2.148.3 | 577k | 544k | 581k | 548k | £3.21bn | 911k |
| microcosm_uk2.89.2 | 510k | 500k | n/a | n/a | £3.30bn | 958k |
| populace_uk2.132.6 | 338k | 338k | 338k | 338k | £1.81bn | 602k |
| populace_uk2.148.3 | 323k | 306k | 323k | 306k | £1.84bn | 602k |
| populace_uk2.89.2 | 253k | 255k | n/a | n/a | £1.34bn | 438k |

Data: populace = Populace UK 2023 (populace-uk-2023-dd68c73-4aa4b14-20260619T023711Z); microcosm = Microcosm UK 2024-25 (microcosm-uk-2024-25-national-20261019T083323Z-6cba5d71).