Inflation

Converting a Dollar Amount Between Two Years’ Purchasing Power

Inflation-adjusted value converts an amount of money from one year’s dollars into another year’s, using the ratio between the two years’ Consumer Price Index values. Enter an amount and two years, and this calculator shows what that amount is equivalent to in the other year’s dollars — “how much is $100 from 1930 worth today?” or “how much would today’s $100 have been worth back in 1980?” It works in either direction: pick an earlier “from” year and a later “to” year to see growth, or the reverse to see how much smaller an amount was worth in the past.

The answer comes from the U.S. Consumer Price Index (CPI-U) — the government’s own measure of how much a broad basket of everyday goods and services costs over time, and the same data source behind most general-purpose inflation calculators.

The Formula

Each year has a published CPI-U index value. The ratio between two years’ index values is exactly how much prices changed between them:

$$\vE{\text{CPI Ratio}} = \frac{\vB{\text{CPI in "To" Year}}}{\vC{\text{CPI in "From" Year}}}$$ $$\text{Equivalent Value} = \vA{\text{Amount}} \times \vE{\text{CPI Ratio}}$$

The average annual rate isn’t simply the total change divided by the number of years — inflation compounds year over year, the same way investment returns do. Instead, it’s the constant yearly rate that, applied repeatedly over the whole period, reproduces the same total change:

$$\text{Average Annual Rate} = \vE{\text{CPI Ratio}}^{1 / \vD{\text{Number of Years}}} - 1$$

Worked Example

$100 in 1980 dollars, converted to 2025 dollars (the most recent complete year this calculator has CPI data for as of this writing):

1. CPI in 1980: $\vC{82.4}$. CPI in 2025: $\vB{321.943}$.
2. Ratio: $\vB{321.943} \div \vC{82.4} \approx \vE{3.907}$.
3. Equivalent value: $\vA{100} \times \vE{3.907} \approx 390.70$.

$100 in 1980 had about the same purchasing power as $390.70 in 2025 — prices roughly quadrupled over that 45-year span, an average of just under 3.2% per year, compounded.

Key Factors to Consider

• CPI-U measures a broad “basket” of goods and services, not any one specific category. Housing, healthcare, groceries, and other individual categories have all risen at different rates than the overall CPI-U average over the decades — this calculator’s figure applies to general purchasing power, not a precise prediction for how any one specific expense has changed.
• Wage growth and inflation are two separate things, easily conflated. This calculator shows how prices have changed, not how income has changed — comparing a past salary to today’s equivalent purchasing power (via this calculator) is a different question from comparing wage growth to inflation over the same period.
• The most recent year’s CPI data reflects a full calendar year, not the current moment. This calculator’s data updates as new official annual figures are published — a partial current year’s inflation isn’t reflected until the full year’s CPI-U figure is officially released.
• Deflation (falling prices) is possible and handled the same way as inflation by this calculator. A CPI ratio below 1 simply produces an equivalent value lower than the original amount — this occasionally happens for specific short periods in economic history, and the math works identically in either direction.

Common Mistakes

• Confusing inflation-adjusted purchasing power with actual wage growth. This calculator only answers “what would this amount buy back then vs. now?” — whether wages kept pace with, outpaced, or fell behind inflation over the same period is a separate comparison this tool doesn’t make on its own.
• Assuming the national CPI-U figure applies evenly to every category of spending. Housing and healthcare have often risen faster than the overall average, while electronics have often risen slower or even fallen in price — a single dollar-for-dollar answer can’t capture that spread.
• Treating the most recent year’s figure as reflecting right now. CPI-U is published for full calendar years — a partial current year’s price changes aren’t in the data until the complete year’s official figure is released.
• Trying to look up a year before 1913. No official CPI-U figure exists before the index was first created that year, so there’s no authoritative government data to calculate against for anything earlier.

Useful to Know

• Want to see how a dollar amount would have grown if invested instead of just tracking prices? The Compound Interest Calculator projects an invested amount forward at an assumed rate of return, a different question from tracking historical inflation.
• Curious how inflation compares to a savings account or investment’s real return? The ROI Calculator shows a plain percentage return that can be compared side by side with this calculator’s average annual inflation rate.
• Comparing prices between two different countries’ currencies rather than two different years? The Currency Converter Calculator handles that instead — a different kind of “what’s this worth” question.