Summary

• Ran the validation Validate PolicyEngine child poverty estimates against RF/OBR benchmarks #1398 asked for and wrote up the results in docs/book/validation/child-poverty-tcl.md.
• PolicyEngine UK's estimate of removing the Universal Credit two-child limit (2029-30):
  • AHC: ~501,000 children lifted from poverty
  • BHC: ~415,000 children lifted
  • Treasury cost: £3.40 bn
• Against the external benchmarks Validate PolicyEngine child poverty estimates against RF/OBR benchmarks #1398 asked us to validate against:
  • OBR EFO November 2025 Table 3.2: 450,000 children lifted, £3.0 bn
  • Resolution Foundation No half measures: 480,000 children lifted, £3.5 bn
• PolicyEngine sits between the two external estimates on the headcount (slightly above OBR, slightly above RF) and on the cost (below RF, above OBR). The agreement is well within the noise from nowcasting / take-up differences.
• Page includes the reproducible code snippet that generated the numbers, three plausible drivers for the small overshoot (nowcasting methodology, marginal take-up assumptions, calibration vintage), and a note on when to re-run.

Notable mechanical detail: the model's baseline already has the TCL removed from 2026-04-06 per Budget 2025 (gov.dwp.universal_credit.elements.child.limit.child_count: .inf), so the validation runs the reverse counterfactual (re-impose the TCL) and reads the sign-positive figures directly.

Test plan

• Code snippet runs end-to-end; figures in the table reproduced.
• Docs build job picks up the new page under validation/.

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