CPI Calculator UK (Official ONS Index)
This CPI calculator uses the official ONS Consumer Prices Index (series D7BT, 2015 = 100) to move a price between any two months or years since 1988. For example, £100 at 2015 prices is £144.10 at September 2026 prices, because the index rose from 100.0 to 144.1. Use it for rent reviews, contract uplifts, pay comparisons and anything else that is linked to CPI.
- Latest CPI index144.1 (Sep 2026)
- CPI annual rate3.5% (Sep 2026)
- Data fromJanuary 1988
Updated November 2026 · Uses ONS CPI index up to September 2026
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How the CPI calculator works
The ONS publishes the CPI as an index where the average for 2015 equals 100. To move a price from one date to another, multiply it by the later index and divide by the earlier one:
New price = old price × CPI (later) ÷ CPI (earlier)
For example, a rent of £850 a month set in September 2025 (index 139.3) uprated to September 2026 (index 144.1) becomes £850 × 144.1 ÷ 139.3 = £879.29, a rise of 3.4%. The calculator does the same sum using the official monthly figures, or the annual average if you choose a whole year.
CPI index by year (2015 = 100)
| Year | CPI annual average | Change on year | £100 then in Sep 2026 |
|---|---|---|---|
| 1988 | 49.6 | – | £291 |
| 1990 | 55.9 | 7.1% | £258 |
| 1995 | 67.2 | 2.6% | £214 |
| 2000 | 72.7 | 0.8% | £198 |
| 2005 | 78.1 | 2.1% | £185 |
| 2010 | 89.4 | 3.2% | £161 |
| 2015 | 100.0 | 0.0% | £144 |
| 2019 | 107.8 | 1.8% | £134 |
| 2020 | 108.7 | 0.8% | £133 |
| 2021 | 111.6 | 2.7% | £129 |
| 2022 | 121.7 | 9.1% | £118 |
| 2023 | 130.5 | 7.2% | £110 |
| 2024 | 133.9 | 2.6% | £108 |
| 2025 | 138.4 | 3.4% | £104 |
The change on year is worked out from the rounded index, so it can differ by 0.1 point from the headline rate the ONS publishes from unrounded data.
Latest monthly CPI figures
| Month | CPI index | 12-month rate |
|---|---|---|
| September 2025 | 139.3 | 3.8% |
| December 2025 | 140.1 | 3.4% |
| March 2026 | 141.0 | 3.3% |
| June 2026 | 142.5 | 2.6% |
| August 2026 | 143.6 | 3.1% |
| September 2026 | 144.1 | 3.5% |
The ONS publishes each month’s CPI about five weeks later, usually on a Wednesday. September CPI is the figure the government normally uses when it reviews benefit and State Pension rates for the following April.
CPI, CPIH and RPI: which index should you use?
- CPI is the main measure of inflation and the one the Bank of England’s 2% target is based on. Most new contracts, pensions and benefits use it.
- CPIH is CPI plus owner occupiers’ housing costs and council tax. It was 144.0 in September 2026, with an annual rate of 3.6%.
- RPI is an older measure that usually runs higher than CPI. It is no longer a National Statistic but is still used for some student loans, older index-linked gilts and some rail fares. The RPI annual rate was 3.9% in September 2026.
- If a lease or contract names an index, use that one. If you want the long-run value of money over a century, use our inflation calculator instead.
Frequently asked questions
What is the current CPI index in the UK?
The CPI index was 144.1 in September 2026 (2015 = 100), the latest figure published by the ONS on 21 October 2026. The 12-month CPI rate was 3.5%.
How do I calculate a CPI increase?
Divide the later CPI index by the earlier one and multiply by your amount. For example, £1,000 from September 2025 (139.3) to September 2026 (144.1) is £1,000 × 144.1 ÷ 139.3 = £1,034.46.
What does 2015=100 mean?
It means the index is scaled so that the average price level in 2015 equals 100. An index of 144.1 means prices are 44.1% higher than the 2015 average.
Which CPI month is used for benefits and pensions?
The September CPI 12-month rate is normally used for the annual uprating of benefits and the State Pension the following April. September 2026 CPI was 3.5%.
How far back does CPI go?
Official CPI index figures run from January 1988. For earlier years, the ONS publishes estimates and long-run series, which our inflation calculator uses to go back to 1900.
Sources and method
We use official UK guidance and recognised formulas, and test each calculator against worked examples. Results are estimates to help you plan, not professional advice. See how we work.