Analysis · April 2026 · ONS HCI December 2025
The official rate is an average. Households on Universal Credit are facing around 3.4%. Working renters are facing around 4.6%. That gap — 1.2 percentage points — is driven by private rent, commuting and childcare.
Main driver: private rent new-lettings divergence (+0.65pp). Then childcare differential (+0.18pp) and commuting (+0.14pp).
ONS official December 2025 · CPIH: 3.6% · Private renters HCI: 3.8% · Social renters HCI: 3.8% · Retired HCI: 3.5%
Custom rates above are modelled estimates built on the ONS HCI series — not official ONS figures.
ONS CPIH was 3.6% in December 2025. That single number covers owner-occupiers, private renters, social renters and retirees in one basket. Here is what it conceals.
In December 2025, the ONS HCI blends for the two groups are nearly identical: WP 3.65%, UC 3.68%. The entire 1.21pp gap comes from five structural adjustments — three that reduce UC's effective rate, two that raise the working-poor rate.
The rent divergence adjustment alone accounts for 54% of the final gap. It reflects a real structural issue: the ONS CPI-04 housing component uses a stock-of-contracts measure that includes all sitting tenancies. New lettings — which working renters face when they move or when a fixed term ends — ran at 8–9% in 2025 according to ONS Private Rental Market Statistics. The base HCI blends being nearly equal in December 2025 means the entire gap is now structural, not driven by any baseline difference in the index series.
Both households are in the bottom half of the income distribution. The difference is in what they pay, what they receive, and where prices are moving fastest.
How the numbers are built. Expand any section for the full calculation.
ONS Household Costs Indices (HCI), Table 1 — monthly 12-month rates by income decile (1–5) and tenure type (social renter, private renter, retired), January 2022 to December 2025 (provisional). This is the primary data source. HCI uses actual price observations for each household group, not a reweighting of aggregate rates. It therefore captures within-category price variation: if decile 1 households buy cheaper food, the food rate for that group reflects cheaper-food inflation.
ONS Living Costs and Food Survey, Workbook 2 (FYE2024) — mean weekly expenditure by income decile (Table A4). Used to derive COICOP category weights for each group. Health (06) and Education (10) are suppressed for low deciles; imputed from the all-households average share.
ONS Consumer Prices Inflation Detailed Reference Tables, Table 8 — CPIH annual rates by COICOP division, used for reference in the methodology. The primary effective rates come from HCI, not from this table × LCFS weights.
ONS Private Rental Market Statistics (PRMS), Q4 2025 — new-lettings rental inflation data used for the private rent divergence adjustment. The ONS confirms its HCI private-rent measure is stock-based, not a new-lettings flow measure.
The UC base blend uses three HCI series, weighted to approximate the UC-eligible working-age population:
Motability adjustment (−0.030pp). Approximately 12% of UC-eligible households include a PIP enhanced-rate mobility component recipient who surrenders the payment to Motability in exchange for a vehicle with all running costs covered. For these households, effective transport inflation ≈ 0%. Transport (COICOP-07) carries a 10.49% weight in the UC basket.
Food substitution adjustment (−0.241pp). ONS scanner data analysis shows budget-tier food inflated roughly 1.5pp below headline food CPI during 2022–25. UC households are concentrated in these product tiers. Food (COICOP-01) carries 16.10% weight.
The working-poor base blend covers income deciles 3–5 and the private renter series:
Private rent divergence (+0.654pp). The ONS CPI private rent measure uses a stock-of-contracts method. New lettings ran at 8–9% in 2025 per ONS PRMS. Working renters face the new-lettings market when they move or renew. The applied uplift: +2.5pp on the COICOP-04 weight.
Commuting adjustment (+0.135pp). LCFS shows ~£1,300/yr commuting spend for employed decile 3–5 households. Annual regulated fares increase: ~2.4% (January 2025). WP annual basket ≈ £22,300.
Childcare differential (+0.175pp). UC households with eligible children have 85% reimbursed (cap: £1,014/month, one child). Working-poor households access only Tax-Free Childcare (20%, capped). Expected net differential across all WP households: ~£1,010/yr. Childcare inflation (CORAM 2025): ~4%.
Error 1 — wrong reference group. The first version blended LCFS "economically inactive non-retired" data (Table A17, Workbook 4) at 30% weight. This ONS category includes early retirees, students and discouraged workers — many of whom are owner-occupiers or private renters, not social renters on UC. The blended housing weight was inflated with a segment of the population structurally different from UC claimants.
Error 2 — aggregate rates applied to heterogeneous categories. COICOP-04 bundles private rent, social rent, mortgage interest, water and fuel. Applying the aggregate CPI-04 rate to a group predominantly on social rent ignores the tenure-specific pattern. April 2024 social rent increases hit around 7.7% (the CPI+1% formula applied to an elevated CPI base); the aggregate rate dilutes this across all tenure types. Switching to the ONS HCI social renter series captures that spike correctly without manual approximation.
Version 2 corrects both errors by building directly on HCI series, which are already group-specific, and limiting the LCFS data to informing blend weights only.
The analysis draws on data from different periods. This is a legitimate concern. Here is what each source contributes and why the combination is defensible:
HCI December 2025 — provides the inflation rates used in both blends. This is the reference point for all effective rate calculations. December 2025 figures are provisional (ONS notation [p]); ONS may revise them at the next quarterly release in May 2026.
LCFS FYE2024 (April 2023–March 2024) — provides the basket composition weights. These weights inform which HCI series to blend and at what proportions, but do not directly affect the rate calculation. Spending shares are slow-moving; the FYE2024 data is the most recent available and is appropriate for this use.
CPI Detailed Reference Tables (Feb 2026) — the component-level CPIH rates (food 3.3%, transport 2.4%, etc.) shown in the methodology for illustration only. They are not the source of the headline effective rates, which come from the HCI series. These rates were included in the original methodology workings section for transparency.
PRMS Q4 2025 — informs the private rent new-lettings divergence. This is the closest available date to the HCI reference period.
The primary finding — a 1.21pp gap between UC and working-poor effective rates — rests on the HCI backbone (December 2025) plus adjustments calibrated to the same period. The cross-date exposure is limited to the rent uplift assumption, which uses a different ONS rent series from the same quarter.
ONS Household Costs Indices, Table 1, October–December 2025 (published February 2026, provisional) · ONS Living Costs and Food Survey, Workbook 2 (expenditure by income), FYE2024 · ONS LCFS Workbook 4 (expenditure by household characteristic), FYE2024 · ONS Consumer Prices Inflation Detailed Reference Tables (February 2026) · ONS UK Private Rental Market Statistics, Q4 2025 · ONS Consumer Price Inflation February 2026 bulletin (CPIH 3.2%) · ONS private rents methodology note (stock-of-contracts vs new lettings) · DWP Universal Credit statistics, March 2024 · Motability Operations Annual Report 2023–24 · JRF / Loughborough University, Minimum Income Standard 2025 · MHCLG Council Tax Statistics for England 2024–25 · NHS England prescription and dental exemptions data 2024 · Ofgem Warm Home Discount scheme 2024–25 · CORAM Family Childcare Survey 2024