Inflation Calculator

How This Calculator Works

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.