An inflation calculator estimates how the purchasing power of money has changed between two years, using a price index such as the CPI. It converts a past amount into today’s equivalent, or the reverse.

It depends on the starting year. Because prices have risen almost every year since the 1940s, $1 from decades ago is generally worth several times more in today’s dollars. Use the calculator above to see the exact estimate.

It’s a well-grounded estimate rather than an exact figure. CPI tracks a broad national average basket of goods, so your own experience of inflation may differ depending on where you live and what you spend money on.

Inflation measures how fast prices rise. Purchasing power measures the flip side: how much a fixed amount of money can actually buy. As inflation rises, purchasing power falls.

A CPI calculator uses the Consumer Price Index — a government-published basket-of-goods price series — to convert money from one year into its equivalent in another. It’s the standard method economists and government agencies use to measure inflation.