A 25% price increase
An index rising from 200 to 250 has a multiplier of 1.25. A basket initially costing 1,000 costs 1,250 later. An unchanged 1,000 later has the buying power of 800 in starting-period currency.
Use an assumed constant inflation rate, or supply two comparable price-index values. No historical CPI dataset or current inflation rate is built in.
USD 1,343.92End amount for same basket
USD 744.09Starting buying power of unchanged amount
34.3916%Cumulative price change
Price-level multiplier
1.343916 ×
A basket costing USD 1,000.00 at the start would cost USD 1,343.92 at the end. Keeping the same nominal amount buys the equivalent of USD 744.09 in starting-period currency.
Projection factor = (1 + rate)^years. Index factor = ending index ÷ starting index. Compare indexes from the same series and base, using consistent annual or monthly observations. An index describes its basket, which can differ from personal spending. Negative rates or falling indexes model deflation.
Your inputs and calculations stay in this browser. No live financial data is fetched; amounts use your selected USD or GBP labels.
How to use the Inflation Calculator
- 01
Choose a constant-rate projection or a comparison of two index values.
- 02
Enter an amount and either elapsed years plus a rate, or starting and ending price indexes.
- 03
Compare the ending cost of the same basket with the starting-period buying power of an unchanged amount.
Examples
An assumed 10% annual rate
At 10% inflation for two years, the price multiplier is 1.21 rather than 1.20 because the second year applies to already increased prices. A 100 basket becomes 121.
Two directions of adjustment
To preserve the same basket, multiply the starting amount by the price-level factor. To express an unchanged later amount in starting-period purchasing power, divide it by that factor. The two results answer different questions, so both are labeled explicitly.
Choosing comparable index values
The ratio method divides the ending index by the starting index. Use the same index series, geographic coverage, and reference base for both. Keep monthly observations separate from annual averages. An index level such as 250 is not itself a 250% inflation rate.
Projection versus measurement
The constant-rate method compounds your chosen rate for the number of years entered; it does not forecast inflation. The index method uses only the two numbers you supply. Neither method includes a historical dataset, automatically selects CPI, or assumes that an average consumption basket matches your spending.
What to know
- No live rates, historical CPI lookup, personal spending model, or exchange-rate conversion.
- Projection allows fractional years using smooth exponential growth; it is not a prediction of future prices.
Common questions
Can prices fall?
Yes. Enter a negative projected rate or an ending index below the starting index. The model then shows deflation: lower equivalent basket cost and higher buying power for an unchanged amount.
Does selecting GBP use a UK inflation series?
No. Currency selection changes the label only. Supply indexes appropriate to your own comparison; no US or UK series is loaded.
Is a 25% price increase a 25% buying-power loss?
No. A factor of 1.25 means an unchanged amount buys 1 ÷ 1.25 = 0.8 of the original basket, a 20% loss of buying power.