Purchasing power is the amount of goods or services a fixed sum of money can actually buy, and it falls whenever prices rise faster than that money does. A 1980 dollar could cover a fast-food meal or most of a tank of gas; the same physical dollar bill today, unless it grew alongside prices, buys a fraction of either. The Consumer Price Index is the tool that measures exactly how fast that erosion happens, and every dollar comparison on this site, from what $100 in 1980 is worth today to the current inflation rate, is purchasing power made visible.
The definition, precisely
Purchasing power is the inverse of the price level: when prices double, a dollar’s purchasing power is cut in half, because it now takes two dollars to buy what one dollar bought before. “Inflation” (prices rising) and “purchasing power falling” describe the same event from two directions, one pointed at goods, the other at money. Economists sometimes call this the real value of money, as opposed to its nominal value, the number printed on the bill, which never changes no matter what it can buy.
How the CPI turns into a purchasing power number
The Bureau of Labor Statistics tracks purchasing power indirectly, by pricing the same basket of goods every month and publishing the result as an index. Divide one year’s index by another’s and you get the ratio by which prices, and therefore purchasing power, have changed between them. The CPI averaged 82.4 in 1980 and 321.9 in 2025, so $100 in 1980 bought what it now takes roughly $391 to buy: a 1980 dollar’s purchasing power was almost four times a 2025 dollar’s. Flip the ratio and a 2025 dollar buys about 26% of what a 1980 dollar bought, which is the same fact stated as loss instead of growth. Run any pair of years through the calculator to see the exact figure for a specific span; the methodology page documents the formula.
A century of erosion, in one number
Stretch the comparison to the full CPI series and the effect compounds dramatically. The index stood at 9.9 in 1913, the year the modern CPI begins, and 321.9 by 2025, a roughly 32-fold increase. That means $100 tucked away in 1913 and left as cash, not invested, had the purchasing power of about $3,250 by 2025. The 1913-to-today comparison is the starkest illustration on this site of why cash alone is a poor long-term store of value: the bills didn’t change, but what they could buy shrank to a fraction of the original.
A single year, up close
Purchasing power doesn’t erode at a constant pace; it tracks whatever the annual inflation rate happens to be. The CPI rose from 270.97 in 2021 to 292.655 in 2022, an annual average increase of about 8.0%, the fastest pace in four decades. A dollar earning zero interest that year lost roughly 7% of its purchasing power in twelve months, meaning $100 saved in a drawer at the start of 2022 could buy what only about $93 would have bought at the start of the year, once translated into 2021 terms. That is the mechanism behind every complaint about savings “not going as far” during a high-inflation year: nothing happened to the money itself, only to what it could be traded for.
Purchasing power, the inflation rate, and the price level aren’t the same thing
Three related ideas get used interchangeably, but they answer different questions. The price level (the CPI itself) is a snapshot: how expensive things are right now relative to the base period. The inflation rate is the price level’s speed: how fast that snapshot is changing, typically measured over 12 months as explained in how inflation is calculated. Purchasing power is what a fixed sum of money can do against that moving backdrop: it falls whenever the inflation rate is positive, stays flat when prices are flat, and actually rises during deflation, when the price level itself falls and a dollar stretches further than it did before.
What keeps purchasing power from falling
Purchasing power only holds steady for a saver, wage earner, or benefit recipient whose income grows at least as fast as prices. That’s why annual raises, Social Security’s cost-of-living adjustment, and interest paid on savings all exist as mechanisms to run alongside inflation rather than get outrun by it: a 3% raise during a year of 4% inflation is nominal growth but a real, if modest, loss of purchasing power. Cash sitting idle, by contrast, has no such mechanism built in, which is the core reason economists distinguish between a dollar’s face value and what it can actually buy.
Why this matters more than the headline number
News coverage tends to report inflation as a single abstract percentage, but purchasing power translates that percentage into something concrete: what a paycheck, a pension, or a pile of cash under a mattress can actually be traded for. It’s also the concept underneath every figure this site publishes. When the calculator says $100 from a given year is “worth” some larger number today, it isn’t claiming that money grew; it’s stating how much money would be needed today to match the purchasing power that $100 carried back then. Every year hub and every year-pair page on this site is, underneath the specific numbers, a purchasing power calculation.