How the inflation calculator works
Inflation is the rate at which prices go up, which means each pound buys a little less every year. This calculator uses the official Consumer Prices Index (CPI) from the Office for National Statistics to show what an amount of money from one year is worth in another. It's the same index the Bank of England uses for its 2% inflation target.
The figures come from ONS series D7BT (CPI index 00: all items, 2015 = 100). For each year from 1988 to 2025 we use the yearly average index, and the latest option uses the September 2026 monthly index of 144.1, published on 21 October 2026. The latest full year included is 2025.
The formula
For example, the CPI index averaged 72.7 in 2000 and 138.4 in 2025. So £100 in 2000 is worth £100 × 138.4 ÷ 72.7 = £190.37 in 2025 prices. Put another way, prices rose by 90.4% over those 25 years, which is an average of 2.61% a year.
The sum works backwards too. To find what £50 today would have been in 2000, multiply by 72.7 ÷ 138.4, which gives £26.26.
What £100 from past years is worth in 2025
| £100 in | CPI index | Worth in 2025 | Average inflation a year |
|---|---|---|---|
| 1990 | 55.9 | £247.58 | 2.62% |
| 1995 | 67.2 | £205.95 | 2.44% |
| 2000 | 72.7 | £190.37 | 2.61% |
| 2005 | 78.1 | £177.21 | 2.90% |
| 2010 | 89.4 | £154.81 | 2.96% |
| 2015 | 100.0 | £138.40 | 3.30% |
| 2020 | 108.7 | £127.32 | 4.95% |
The jump in the 2020s stands out. Between the 2021 and 2023 yearly averages the index rose from 111.6 to 130.5, so £250 in 2021 needed £292.34 in 2023 to buy the same things. The yearly CPI rate peaked at 11.1% in October 2022, the highest for 41 years, before falling back.
Why the answer may differ from other calculators
- CPI vs RPI: the Retail Prices Index usually shows higher inflation than CPI because of the way it's calculated and because it includes mortgage interest. The ONS no longer treats RPI as a national statistic, but it's still used for some things such as student loan interest and some index-linked bonds. This calculator uses CPI only.
- Yearly averages vs single months: we compare yearly averages, which smooths out monthly ups and downs. A calculator that compares, say, January 2000 with January 2025 will give a slightly different figure.
- Your own inflation rate: CPI tracks a typical basket of goods and services. If you spend more than average on energy, rent or food, your personal inflation rate may be higher or lower.
Using inflation figures in real life
Comparing a salary or a price with inflation tells you whether it has gone up in real terms. If your pay was £25,000 in 2015, you'd need £34,600 in 2025 to have the same buying power (25,000 × 138.4 ÷ 100). The pay rise calculator checks a single year's rise against the latest CPI rate.
Inflation also matters for savings. Money in a current account paying no interest loses value every year, so a savings rate below inflation is a real-terms loss. Use the savings calculator or the compound interest calculator to see whether your savings are growing faster than prices.
Frequently asked questions
What is £100 in 2000 worth today?
Using ONS CPI yearly averages, £100 in 2000 is worth £190.37 in 2025 prices, because the index rose from 72.7 to 138.4. Using the September 2026 index of 144.1, it's £198.21.
What is the UK inflation rate now?
CPI inflation was 3.5% in the 12 months to September 2026, up from 3.1% in August, according to the Office for National Statistics release of 21 October 2026.
Which inflation measure does this calculator use?
It uses the Consumer Prices Index, ONS series D7BT, with 2015 as the base year (2015 = 100). It's the measure the Bank of England targets at 2%.
How much has inflation gone up since 2020?
The yearly average CPI index rose from 108.7 in 2020 to 138.4 in 2025, an increase of 27.3%. So something that cost £100 in 2020 cost about £127 in 2025.
Why does the calculator start in 1988?
The official ONS CPI index (D7BT) has yearly figures from 1988. Before that, the ONS uses estimates and other indices such as the Retail Prices Index, which aren't directly comparable.
Last reviewed October 2026 using 2026/27 figures. This calculator gives an estimate for guidance only.