What inflation is, in one paragraph
Inflation is a broad increase in prices across the economy, which means the same dollar buys less over time. Economists don't measure it from a single item — a $1.99 gallon of milk tells you nothing about the whole basket. Instead the Bureau of Labor Statistics tracks the Consumer Price Index (CPI-U), a weighted basket of about 80,000 goods and services. The Federal Reserve targets 2% average annual inflation on the closely related PCE index.
The math behind purchasing power
If the average annual inflation rate is i and you want to project an amount P forward n years: Future nominal = P · (1 + i)^n. To go the other way — see how much a past dollar is worth today — divide instead of multiply: Present value = P / (1 + i)^n. At 3% inflation, $100 today grows to about $181 in 20 years, or a $100 bill from 2005 buys roughly $70 of goods today.
Worked example
Suppose your grandparents put $500 in a birthday card in 1985. At an average U.S. inflation rate of 2.7% between 1985 and 2025 (40 years): $500 × (1.027)^40 ≈ $1,450. That's what you'd need today to buy what $500 bought in 1985 — a fifth of a modest new car, a couple months of urban rent, or a decent bike.
| Inflation rate | In 10 years | In 20 years | In 30 years |
|---|---|---|---|
| 2% | $12,190 | $14,859 | $18,114 |
| 3% | $13,439 | $18,061 | $24,273 |
| 4% | $14,802 | $21,911 | $32,434 |
| 6% | $17,908 | $32,071 | $57,435 |
Real vs. nominal dollars
The number on a paycheck or a bond coupon is nominal. What that number buys in today's goods is real. A 5% raise in a year of 6% inflation is a 1% pay cut in real terms. When you see a chart of home prices, GDP, or CEO pay over decades, always check whether it's real or nominal — the difference across 30 years can be an entire order of magnitude. Financial planners work in real dollars because that's what actually funds your retirement.
What has historically kept up with inflation
- Broad stock indexes (S&P 500) have averaged 6%–7% real returns over century-long spans.
- Treasury Inflation-Protected Securities (TIPS) explicitly adjust principal to CPI-U.
- I bonds, capped at $10,000 per person per year, pay a fixed rate plus the CPI-U inflation rate.
- Long-duration fixed-rate cash (a 30-year bond, a savings account) is the worst — you lock in a nominal rate while prices rise around you.
Why 2% and not zero?
Central banks target mild positive inflation because zero inflation risks tipping into deflation, which discourages spending (why buy today if it will be cheaper tomorrow?) and makes debt harder to repay. The 2% target — used by the U.S. Federal Reserve, the ECB, and the Bank of Japan — is high enough to keep nominal interest rates comfortably positive, giving central banks room to cut during a recession.
Common mistakes with inflation math
- Adding annual rates instead of compounding them (3% for 10 years is 34%, not 30%).
- Confusing the inflation rate with the change in the index itself.
- Using headline CPI when your budget looks nothing like the average basket — retirees, for example, feel healthcare inflation harder than the national average.
- Assuming past averages will hold — the 1970s averaged 7.4% U.S. inflation; the 2010s averaged 1.8%.
How to use this inflation calculator
- Enter the dollar amount you want to convert.
- Enter the number of years — forward for a projection, backward for a historical comparison.
- Enter the annual inflation rate. Use the U.S. long-run average (about 3%) if you're planning; use a specific year's CPI change for accuracy.
- Read both the future nominal value and today's equivalent purchasing power.
Related calculators
Pair the inflation calculator with the compound interest calculator to see whether an expected investment return actually beats inflation, the retirement calculator to model a 30-year nest egg in real dollars, the investment calculator for lump-sum vs. periodic contribution comparisons, and the salary calculator to check whether next year's raise keeps pace with the cost of living.