Correct the protected pension-age Housing Benefit lone-parent allowance projection #2155

Summary

PolicyEngine UK 2.106.1 does not faithfully represent the weekly Housing Benefit personal allowance selected by gov.dwp.housing_benefit.allowances.lone_parent.aged. The parameter back-carries the 2019-20 rate of £181 into 2015-16 through 2018-19, when the regulations used two pension-age tiers, omits the 2020-21 rate of £187.75, and stores £239.20 instead of the enacted £244.40 for 2025-26. Pull request #1925 already owns the 2020 and 2025 corrections and the corrected SI 2006/214 source; the earlier period requires a separate tiered formula rather than writing one historical series into this parameter. From April 2021, this branch is the protected rate for a lone parent who attained pensionable age before 1 April 2021, while later claimants receive the lower standard-minimum-guarantee amount; pull request #1913 owns that routing. The protected 2026-27 rate is the £238 guarantee plus the retained £17.96 maximum Savings Credit uplift, rounded to £256. Projecting that composite rate wholly by CPI from 2027-28 therefore misses the guarantee's earnings basis. A transparent forecast should combine the non-negative May-to-July earnings input for the guarantee with September CPI for the retained uplift, using published ONS observations when available and the model's OBR-backed forecasts otherwise, while making clear that no 2027-28 amount has been enacted. Proposed benefit and pension rates 2015 to 2016 (page 6, Housing Benefit table, Pensioner single/lone parent 65 or over row); Proposed benefit and pension rates 2016 to 2017 (Housing Benefit table, Pensioner single/lone parent 65 or over row); Proposed benefit and pension rates 2017 to 2018 (Housing Benefit table, Pensioner single/lone parent 65 or over row); Proposed benefit and pension rates 2018 to 2019 (Housing Benefit table, Pensioner single/lone parent 65 or over row); Benefit and pension rates 2019 to 2020 (Housing Benefit table, Pensioner single/lone parent 65 or over row); Benefit and pension rates 2020 to 2021 (Housing Benefit, Pensioner, personal allowances table); Benefit and pension rates 2021 to 2022 (Housing Benefit, Pensioner, personal allowances table); Proposed benefit and pension rates 2022 to 2023 (Housing Benefit, Pensioner, personal allowances table); Benefit and pension rates 2024 to 2025 (Housing Benefit, personal allowances, State Pension age table); Benefit and pension rates 2025 to 2026 (Housing Benefit, personal allowances, State Pension age table); Benefit and pension rates 2026 to 2027 (Housing Benefit, personal allowances, State Pension age table; Pension Credit table); The Social Security Benefits Up-rating Order 2026 (Schedule 6, amendment of Schedule 3 paragraph 1(1)(b) and (c) to SI 2006/214); The Social Security Benefits Up-rating Order (Northern Ireland) 2026 (Schedule 6, amendment of Schedule 4 paragraph 1(1)(b) and (c) to SR 2006/406); The Housing Benefit (Persons who have attained the qualifying age for state pension credit) (Amendment) Regulations 2021 (regulation 2(2) and (3)); Explanatory memorandum to SI 2021/188 (paragraphs 7.1 through 7.5); Social Security Administration Act 1992 section 150 (section 150(1)(l), (2), and (3)); Social Security Administration Act 1992 section 150A (section 150A(1)(d), (2), (3), (4), and (8)); A14/2025 Housing Benefit uprating for the financial year ending March 2027 (paragraphs 5 and 6); Average weekly earnings, whole economy total pay, three-month average growth on a year earlier (series KAC3, May to July 2026 first estimate, 3.9%); CPI annual rate, all items (series D7G7; September annual rate used for the following April uprating); Economic and fiscal outlook March 2026 (detailed forecast tables, receipts table 3.19 September CPI and economy table 1.6 quarterly earnings)

Audited model surface

• Audited release: policyengine-uk 2.106.1
• Audit unit: parameter:gov.dwp.housing_benefit.allowances.lone_parent.aged
• Last model modification: 2026-05-23
• Audit date: 2026-10-05
• Periods reviewed: 2015-16 through 2026-27 explicit values, 2021-22 and later cohort routing, 2027-28 and later projection behavior
• Jurisdictions: Great Britain, Northern Ireland

Findings and implementation parts

1. The release's one undifferentiated branch cannot represent the two pension-age tiers used before April 2019: for example, the published 2015-16 rates distinguish a claimant over qualifying age but under 65 from one aged 65 or over. It also omits the 2020-21 £187.75 amount and stores £239.20 instead of £244.40 for 2025-26. Pull request #1925 owns the explicit 2020 and 2025 corrections and documents the remaining pre-2019 structural gap.

Sources: Proposed benefit and pension rates 2015 to 2016 (page 6, Housing Benefit table, Pensioner single/lone parent 65 or over row); Proposed benefit and pension rates 2016 to 2017 (Housing Benefit table, Pensioner single/lone parent 65 or over row); Proposed benefit and pension rates 2017 to 2018 (Housing Benefit table, Pensioner single/lone parent 65 or over row); Proposed benefit and pension rates 2018 to 2019 (Housing Benefit table, Pensioner single/lone parent 65 or over row); Benefit and pension rates 2019 to 2020 (Housing Benefit table, Pensioner single/lone parent 65 or over row); Benefit and pension rates 2020 to 2021 (Housing Benefit, Pensioner, personal allowances table); Benefit and pension rates 2021 to 2022 (Housing Benefit, Pensioner, personal allowances table); Proposed benefit and pension rates 2022 to 2023 (Housing Benefit, Pensioner, personal allowances table); Benefit and pension rates 2024 to 2025 (Housing Benefit, personal allowances, State Pension age table); Benefit and pension rates 2025 to 2026 (Housing Benefit, personal allowances, State Pension age table); Benefit and pension rates 2026 to 2027 (Housing Benefit, personal allowances, State Pension age table; Pension Credit table)

• Preserve pull request Set DWP benefit rates to the announced amounts, not CPI projections #1925's correction to £187.75 for 2020-21 and £244.40 for 2025-26, its corrected GB and Northern Ireland sources, and its description limiting this branch to the protected pre-April 2021 cohort. Do not write the 2015-18 age-65-and-over rates directly into this branch without also implementing the historical lower tier and its age selector; that structural work belongs to the enqueued applicable-amount formula reviews. Benefit and pension rates 2020 to 2021 (Housing Benefit, Pensioner, personal allowances table); Benefit and pension rates 2025 to 2026 (Housing Benefit, personal allowances, State Pension age table)
  • Add or update reference at policyengine_uk/parameters/gov/dwp/housing_benefit/allowances/lone_parent/aged.yaml → description, values.2020-04-01, values.2025-04-01, and metadata.reference using Benefit and pension rates 2020 to 2021 (Housing Benefit, Pensioner, personal allowances table); Benefit and pension rates 2025 to 2026 (Housing Benefit, personal allowances, State Pension age table); Benefit and pension rates 2026 to 2027 (Housing Benefit, personal allowances, State Pension age table; Pension Credit table).

2. The release selects the higher aged allowance whenever any member is over State Pension age. From 1 April 2021, a lone parent who attained State Pension age on or after that date instead receives the lower amount; in 2026-27 the two weekly rates are £256 and £238. Pull request #1913 already implements this cohort split for Housing Benefit and the differing national Council Tax Reduction rules.

Sources: The Housing Benefit (Persons who have attained the qualifying age for state pension credit) (Amendment) Regulations 2021 (regulation 2(2) and (3)); Explanatory memorandum to SI 2021/188 (paragraphs 7.1 through 7.5); The Social Security Benefits Up-rating Order 2026 (Schedule 6, amendment of Schedule 3 paragraph 1(1)(b) and (c) to SI 2006/214); The Social Security Benefits Up-rating Order (Northern Ireland) 2026 (Schedule 6, amendment of Schedule 4 paragraph 1(1)(b) and (c) to SR 2006/406)

• Reuse pull request Split pension-age Housing Benefit allowances by when State Pension age was attained #1913's separate post-cutoff parameters and its claimant-attainment-date routing in the Housing Benefit and Council Tax Reduction applicable-amount formulas. Do not duplicate that structural correction in the historical-and-projection pull request. The Housing Benefit (Persons who have attained the qualifying age for state pension credit) (Amendment) Regulations 2021 (regulation 2(2) and (3)); Explanatory memorandum to SI 2021/188 (paragraphs 7.1 through 7.5); The Social Security Benefits Up-rating Order 2026 (Schedule 6, amendment of Schedule 3 paragraph 1(1)(b) and (c) to SI 2006/214); The Social Security Benefits Up-rating Order (Northern Ireland) 2026 (Schedule 6, amendment of Schedule 4 paragraph 1(1)(b) and (c) to SR 2006/406)
  • Add or update reference at policyengine_uk/variables/gov/dwp/housing_benefit/housing_benefit_applicable_amount.py → formula pension-age lone-parent allowance selection using The Housing Benefit (Persons who have attained the qualifying age for state pension credit) (Amendment) Regulations 2021 (regulation 2(2) and (3)); Explanatory memorandum to SI 2021/188 (paragraphs 7.1 through 7.5).
  • Add or update reference at policyengine_uk/variables/gov/local_authorities/council_tax_reduction/council_tax_reduction_applicable_amount.py → formula pension-age lone-parent allowance selection using The Housing Benefit (Persons who have attained the qualifying age for state pension credit) (Amendment) Regulations 2021 (regulation 2(2) and (3)); Explanatory memorandum to SI 2021/188 (paragraphs 7.1 through 7.5).

3. The higher allowance is based on the Pension Credit standard minimum guarantee plus the maximum Savings Credit. In 2026-27 those published components are £238 and £17.96, and the enacted Housing Benefit amount is £256 after rounding. DWP uprated the guarantee by 4.8% for 2026-27 and the maximum Savings Credit by 3.8% CPI. The release instead applies one CPI index to the whole £256 after 2026, yielding about £261.89 in 2027. Current main has a provisional 3.9% May-to-July 2026 earnings observation and an OBR-backed 2.1157% September 2026 CPI forecast. A composite that allocates the enacted base as a £238 guarantee and an £18 retained uplift therefore yields about £265.66 for 2027; a pure earnings index would also be inexact because it would apply earnings growth to the retained uplift.

Sources: Explanatory memorandum to SI 2021/188 (paragraphs 7.1 through 7.5); Benefit and pension rates 2026 to 2027 (Housing Benefit, personal allowances, State Pension age table; Pension Credit table); Social Security Administration Act 1992 section 150 (section 150(1)(l), (2), and (3)); Social Security Administration Act 1992 section 150A (section 150A(1)(d), (2), (3), (4), and (8)); A14/2025 Housing Benefit uprating for the financial year ending March 2027 (paragraphs 5 and 6); Average weekly earnings, whole economy total pay, three-month average growth on a year earlier (series KAC3, May to July 2026 first estimate, 3.9%); CPI annual rate, all items (series D7G7; September annual rate used for the following April uprating); Economic and fiscal outlook March 2026 (detailed forecast tables, receipts table 3.19 September CPI and economy table 1.6 quarterly earnings)

• Add a single/lone-parent higher-allowance forecast index that combines a £238 component following the non-negative May-to-July average-weekly- earnings statutory input with an £18 component following the September CPI statutory input. Those inputs use published ONS observations when available and OBR-backed forecasts otherwise. Use the index for both the single and lone-parent aged parameters after 2026, document that it is a modelling assumption rather than an enacted future rate, and add focused tests for the generated index and both parameters. Explanatory memorandum to SI 2021/188 (paragraphs 7.1 through 7.5); Benefit and pension rates 2026 to 2027 (Housing Benefit, personal allowances, State Pension age table; Pension Credit table); Social Security Administration Act 1992 section 150 (section 150(1)(l), (2), and (3)); Social Security Administration Act 1992 section 150A (section 150A(1)(d), (2), (3), (4), and (8)); A14/2025 Housing Benefit uprating for the financial year ending March 2027 (paragraphs 5 and 6); Average weekly earnings, whole economy total pay, three-month average growth on a year earlier (series KAC3, May to July 2026 first estimate, 3.9%); CPI annual rate, all items (series D7G7; September annual rate used for the following April uprating); Economic and fiscal outlook March 2026 (detailed forecast tables, receipts table 3.19 September CPI and economy table 1.6 quarterly earnings)
  • Add or update reference at policyengine_uk/parameters/gov/dwp/housing_benefit/allowances/lone_parent/aged.yaml → metadata.uprating using Explanatory memorandum to SI 2021/188 (paragraphs 7.1 through 7.5); Benefit and pension rates 2026 to 2027 (Housing Benefit, personal allowances, State Pension age table; Pension Credit table); Social Security Administration Act 1992 section 150 (section 150(1)(l), (2), and (3)); Social Security Administration Act 1992 section 150A (section 150A(1)(d), (2), (3), (4), and (8)); A14/2025 Housing Benefit uprating for the financial year ending March 2027 (paragraphs 5 and 6); Average weekly earnings, whole economy total pay, three-month average growth on a year earlier (series KAC3, May to July 2026 first estimate, 3.9%); CPI annual rate, all items (series D7G7; September annual rate used for the following April uprating); Economic and fiscal outlook March 2026 (detailed forecast tables, receipts table 3.19 September CPI and economy table 1.6 quarterly earnings).
  • Add or update reference at policyengine_uk/parameters/gov/dwp/housing_benefit/allowances/lone_parent/aged.yaml → description and metadata.reference using Explanatory memorandum to SI 2021/188 (paragraphs 7.1 through 7.5); Benefit and pension rates 2026 to 2027 (Housing Benefit, personal allowances, State Pension age table; Pension Credit table); Social Security Administration Act 1992 section 150 (section 150(1)(l), (2), and (3)); Social Security Administration Act 1992 section 150A (section 150A(1)(d), (2), (3), (4), and (8)); A14/2025 Housing Benefit uprating for the financial year ending March 2027 (paragraphs 5 and 6); Average weekly earnings, whole economy total pay, three-month average growth on a year earlier (series KAC3, May to July 2026 first estimate, 3.9%); CPI annual rate, all items (series D7G7; September annual rate used for the following April uprating); Economic and fiscal outlook March 2026 (detailed forecast tables, receipts table 3.19 September CPI and economy table 1.6 quarterly earnings).

Projection behavior

• gov.dwp.housing_benefit.allowances.lone_parent.aged uses gov.benefit_uprating_cpi after 2026-04-01 (first projected date 2027-04-01): incorrect_in_release. CPI-only uprating does not preserve the higher allowance's two-component policy basis: its standard-minimum-guarantee component currently follows earnings while its retained Savings Credit component follows prices. Sources: Explanatory memorandum to SI 2021/188 (paragraphs 7.1 through 7.5); Benefit and pension rates 2026 to 2027 (Housing Benefit, personal allowances, State Pension age table; Pension Credit table); Social Security Administration Act 1992 section 150 (section 150(1)(l), (2), and (3)); Social Security Administration Act 1992 section 150A (section 150A(1)(d), (2), (3), (4), and (8)); A14/2025 Housing Benefit uprating for the financial year ending March 2027 (paragraphs 5 and 6); Average weekly earnings, whole economy total pay, three-month average growth on a year earlier (series KAC3, May to July 2026 first estimate, 3.9%); CPI annual rate, all items (series D7G7; September annual rate used for the following April uprating); Economic and fiscal outlook March 2026 (detailed forecast tables, receipts table 3.19 September CPI and economy table 1.6 quarterly earnings)

Uncertainties and exclusions

No 2027-28 Housing Benefit personal allowance had been enacted or published in an official rates table by 5 October 2026. The proposed composite is a forecast convention, not a prediction of the eventual order: section 150A leaves the Secretary of State to estimate earnings and permits rounding or a larger increase, while section 150 reviews but does not unconditionally require a CPI increase to the Savings Credit amounts. Northern Ireland makes corresponding orders. The release stores one United Kingdom parameter, so this review does not certify each earlier Northern Ireland instrument separately. Pull request #1925 owns the 2020-21 and 2025-26 values and source correction, pull request #1913 owns the post-2021 cohort and Council Tax Reduction routing, and the enqueued applicable-amount formula reviews own the earlier two-tier gap. The shared single/lone-parent projection correction uses current main's statutory uprating inputs; draft pull request #2146 should reuse the same May-to-July earnings input when it rebases. The 3.9% earnings figure is the September 2026 first estimate and may be revised in the October release, while September 2026 CPI is still an OBR-backed forecast. This review does not certify premiums, income, capital, entitlement, benefit-cap, or claim-propensity rules.