UK Inflation Calculator

What would an old sum of money be worth now? This calculator converts an amount between any two years using the Office for National Statistics price indices, reports total and annual inflation over the period, and shows how much purchasing power a fixed sum has lost.

How inflation converts money between years

A price index sets a reference point at 100 and expresses every other period relative to it. The CPI all items series, ONS code D7BT, uses 2015 as its base, so an index of 135 means the basket costs 35% more than in 2015. The RPI all items series, code CHAW, works the same way but is based on the single month of January 1987, which is why its level is much higher. The levels of the two series cannot be compared with each other, because they start from different points; only the percentage change within one series means anything, and the calculator only divides two levels from the series you select.

Converting money between two years is then one division. Divide the later index by the earlier one to get the ratio between the two years’ money, and multiply your amount by it. From 100 to 135 the ratio is 1.35, so £1,000 becomes £1,350. In the other direction, £1,000 in the later year has the spending power of about £741 in earlier-year money.

That second figure is the one people underestimate. Total inflation of 35% does not remove 35% of your purchasing power; it removes about 26%, because the loss is measured against the larger, later number. Mixing up the two directions is the most common mistake in inflation comparisons.

Total inflation versus annual inflation

A 35% rise sounds alarming until you spread it over eleven years, when it is under 2.8% a year. A modest-sounding 4% a year, on the other hand, compounds to about 48% over a decade. Both are true; which is useful depends on the question.

For judging a pay rise, the annual figure is the one to beat: if inflation ran at 2.8% and your rise was 2%, your pay fell in real terms. For a long-held cash balance or a fixed pension, the total figure shows the gap that has actually opened up. The tool reports both, along with the index ratio so you can check the arithmetic.

CPI, RPI and which one to use

CPI is the headline measure. The Bank of England targets it at 2%, benefits are uprated by it, it is one of the three tests in the State Pension triple lock, and it is what most commentary means by the inflation rate. RPI is an older measure that includes mortgage interest and council tax and uses a different averaging formula, so it tends to run above CPI, historically by around a percentage point.

RPI lost its status as a national statistic and is due to be aligned with CPIH from 2030, but many contracts still refer to it, including index-linked gilts, some commercial leases, regulated rail fares and student loan interest. If you are checking a figure a contract calculates, use the measure the contract names.

Because both series are published by the ONS rather than fixed by law, the tool stores the series codes and the CPI base as parameters and asks you for the two index levels. You can see exactly which two numbers produced the answer and check them against the ONS website.

Using the average rate method

When the period runs into the future there is no index to look up. Switching to an average annual rate compounds a percentage over the years between your dates instead, which suits questions such as what a £30,000 income needs to become in fifteen years to keep its value, or what a fixed annuity will be worth late in retirement.

Treat the result as a scenario. Actual inflation is uneven: the UK saw years close to zero in the mid-2010s and around 9% in 2022, and an average hides that. Running the calculation at two or three rates gives a more honest range than one number.

Why your own inflation rate differs

A price index follows a basket weighted to the average household, and nobody is the average household. If a large share of your spending goes on rent, energy, food or childcare and those prices rise faster than the index, your personal inflation rate is higher than the published one, sometimes by several percentage points when energy prices move sharply.

This is systematic. Lower-income households spend a bigger share of their budget on essentials, which were the categories that rose most in 2022 and 2023, so they faced higher inflation than the headline figure. Higher-income households, with more discretionary spending, faced less. The index averages them, so treat the equivalent amount as a benchmark rather than a measure of what happened to your own money.

What this UK inflation calculator shows

The chart traces your amount from the start year to the end year at the implied annual rate, finishing on the equivalent amount. Because inflation compounds, the gap between the original sum and the rising line widens each year, which over a decade or more is the main argument for holding long-term savings in something that grows rather than in cash.

Use the results for planning and comparison. This is not financial advice, and an index average will never exactly match the inflation a particular household experiences.

About This UK Inflation Calculator

Use this UK inflation calculator to get an instant, accurate estimate. The figures follow official guidance and every rate and threshold is kept up to date for 2026. Adjust the inputs above to match your situation, or browse all our calculators to plan your next step.