Methodology: United Kingdom

Official data verified · CPI (ONS) · Annual average · Not seasonally adjusted · Data through September 2026 (fetched 2026-11-02) · CPI All items (D7BT), MM23 dataset

The data

All British figures come from the Consumer Price Index published by Office for National Statistics (CPI All items (D7BT), MM23 dataset; base period 2015=100). ONS data are published under the Open Government Licence v3.0. This site is not affiliated with Office for National Statistics.

Basis

Calculations use the not-seasonally-adjusted index, as published in the MM23 dataset. The UK CPI is published monthly from 1988. For longer horizons this site also shows the RPI (from 1987 in index form) and CPIH — always as separate series, never blended with CPI: the three measures have different baskets and methods, and RPI is no longer a headline measure. UK pages therefore start in 1988 rather than splicing older modelled estimates into the official series.

The formula

Adjusted amount = amount × (index at end ÷ index at start). Formula v1.0 — annual-average CPI, NSA (per-country basis on each methodology page). Year pages compare annual averages (the mean of a year's published values); the current year's average covers only the periods published so far and is labeled partial. The change in the price level and the change in purchasing power are stated as two separate numbers, because they are not the same: if prices rise 100%, purchasing power falls 50%.

See also the general methodology and the data updates log.