Inflation Calculator - US and UK Purchasing Power Over Time

Supported inflation series and date coverage

The calculator supports two headline consumer price indices published by official statistical agencies:

• US CPI (BLS): all-items Consumer Price Index for urban consumers, published by the U.S. Bureau of Labor Statistics. Annual data runs from approximately 1913 to the most recent available year.
• UK CPI (ONS): all-items Consumer Prices Index, published by the UK Office for National Statistics. Annual data runs from the mid-20th century onward.

Data are loaded as annual CPI index levels by calendar year. The earliest year available depends on the selected series.

What is inflation?

Inflation is a general rise in prices over time and a corresponding fall in the purchasing power of money. When inflation runs at 3% per year, something that costs $100 today costs roughly $103 next year. Compounded over decades the effect is large: the US CPI has risen approximately 30 times since 1913, equivalent to an average annual rate of about 3.2%.

The opposite is deflation, a general fall in prices, where a fixed amount of money buys more over time. Very rapid inflation over short periods is called hyperinflation. In the US, annual CPI peaked at about 14.8% in early 1980 and more recently reached 8.3% in 2022, the highest since 1981.

How the calculation works

Both dates are mapped to calendar years. The calculator looks up the CPI index level for each year. If the start year has index CPI_start and the comparison year has index CPI_end, then an amount A in start-year prices corresponds to:

A × CPI_end / CPI_start

For the yearly table, the calculator steps year by year between the two dates and applies each year's CPI change to the running value. Inflation increases the nominal figure; deflation decreases it.

Worked example

What would $1,000 in 1980 be worth in 2020 prices? The US CPI index (base 1982-84=100) was approximately 82.4 in 1980 and 258.8 in 2020.

$1,000 × 258.8 / 82.4 ≈ $3,140

This means a basket of goods and services that cost $1,000 in 1980 would cost roughly $3,140 in 2020. Prices more than tripled over those 40 years, corresponding to an average annual inflation rate of about 2.9%.

Average annual inflation rate

The calculator reports the geometric average rate that links the starting value to the final value over the period. If the starting value is V_start, the final value V_end, and the period is n years, the rate r satisfies:

V_end = V_start × (1 + r)^n

For the 1980-to-2020 example: (3.140)^(1/40) - 1 ≈ 2.9% per year. This geometric average smooths out year-to-year volatility into a single comparable figure.

Forward and backward calculations

• Forward: "What would $100 in 1950 cost in 2010 prices?" The CPI ratio scales the amount up.
• Backward: "What did $100 in 2010 correspond to in 1950 prices?" The CPI ratio scales the amount down.

Both directions use the same CPI ratio, so the math stays consistent whether inflation is low, high, or negative. Switching the two dates gives you the inverse result.

Reading the results

• The summary shows starting amount, final value, total and percentage change, and the average annual inflation rate across the period.
• The chart plots the inflation-adjusted value over time alongside the annual inflation rate, using 0% as the baseline.
• The year-by-year table lists each year's inflation rate, the monetary change on your amount, and the updated cumulative value.

Important assumptions and limitations

• Average basket: CPI reflects average household spending. If you spend heavily on housing or healthcare, your personal inflation rate may be higher than the headline index.
• Method changes: CPI weights and methods are revised over time. Comparisons spanning many decades, such as 1930 to 2020, are approximate because the basket composition has changed substantially.
• Annual data only: the calculator uses annual index levels, not monthly data. Within-year dates are mapped to the same calendar-year index.
• No wages or returns: the tool only adjusts a fixed nominal amount for CPI. It does not model wage growth, savings returns, or investment performance.
• No extrapolation: results stop at the last available CPI year. Future inflation is not projected.

Supporting calculators

• Salary growth vs. inflation: use the Salary Increase Calculator to measure nominal pay raises and compare real income progress after inflation.
• Retirement purchasing power: use the Retirement Calculator to see how inflation changes a future retirement balance and income target.
• Savings vs. inflation: use the Savings Calculator to test whether your savings path is likely to keep up with inflation over time.

Learn more

• CPI data transparency: read the Data Guide for source and methodology details behind the inflation datasets used here.
• Salary and purchasing power: read the Salary Guide to understand how inflation affects real wages, how to compare pay in real terms, and what a raise actually means after prices rise.