Inflation is the general rise in prices over time, which means each dollar buys a little less than it used to. At a steady 3% a year, $10,000 kept in cash for 10 years would buy only what about $7,440.94 buys today. The same rate roughly halves purchasing power in 24 years, using the Rule of 72. To keep up, your savings need to earn more than the rate at which prices are rising, after tax.
Below we show how the main U.S. price index is built, how to measure what rising prices do to your own money, and how to compare returns honestly.
How is inflation measured in the United States?
The most widely quoted measure is the Consumer Price Index, published monthly by the Bureau of Labor Statistics. BLS tracks the prices of a fixed basket of goods and services that urban consumers buy, including food, housing, apparel, transportation, medical care and recreation, and reports how the cost of that basket changes. The headline figure most news reports cite is the 12-month change in the CPI for All Urban Consumers.
BLS also publishes “core” CPI, which excludes food and energy because their prices swing more from month to month. The Federal Reserve, for its part, states a longer-run goal of 2% inflation measured by a different index, the price index for personal consumption expenditures.
How much purchasing power do you lose each year?
To find what a sum will buy in the future in today’s dollars, divide it by (1 + rate) raised to the number of years:
- Real value = Amount ÷ (1 + rate)^years
- $10,000 ÷ 1.03^10 = $10,000 ÷ 1.3439 ≈ $7,440.94
Going the other way, a basket that costs $100 today costs $100 × 1.03^5 ≈ $115.93 in five years at the same rate. These figures assume a constant rate; real-world price growth varies year to year.
The inflation calculator runs both directions, so you can check what a past salary is worth now or what you will need in the future.
What is the Rule of 72?
Divide 72 by the annual rate to estimate how many years it takes for prices to double, or for purchasing power to halve. At 3%, that is 72 ÷ 3 = 24 years. At 6%, it is 12 years. It is an approximation, but a close one for rates in the single digits, and it makes the long-run effect easy to picture.
What is a real rate of return?
Your nominal return is what an account statement shows. Your real return is what is left after rising prices. The precise formula is:
- Real return = (1 + nominal return) ÷ (1 + inflation rate) − 1
If a savings account pays 4% and prices rise 3%, the real return is 1.04 ÷ 1.03 − 1 ≈ 0.97%, slightly less than the shortcut of 4% − 3% = 1%. Taxes reduce it further: if that 4% interest is taxed at 22%, you keep 3.12%, and the real after-tax return is 1.0312 ÷ 1.03 − 1 ≈ 0.12%.
Compare long-run growth in the compound interest calculator, entering your expected rate minus the price-growth rate to see results in today’s dollars.
Which investments help protect against rising prices?
No investment is guaranteed to beat price growth every year, but a few are built with it in mind:
- Treasury Inflation-Protected Securities (TIPS): the principal is adjusted with the CPI, and interest is paid on the adjusted principal.
- Series I savings bonds: the rate combines a fixed rate with a variable rate that resets every six months based on the CPI.
- Stocks and real estate have historically outpaced rising prices over long periods, but with much more short-term risk.
Cash in a checking account typically loses ground. That does not mean you should hold none, since an emergency fund needs to be safe and available, but long-term savings usually need growth.
How does inflation affect retirement planning?
A retirement that lasts 25 or 30 years spans a lot of price increases. If you need $50,000 a year in today’s dollars and prices rise 3% a year, you would need about $67,196 in year 11 to buy the same things. Social Security benefits get annual cost-of-living adjustments based on a CPI measure, but most private pensions and fixed annuities do not. Model this with the retirement calculator, entering an expected rate of price growth rather than leaving it at zero.
How should you use these numbers in everyday decisions?
- When you negotiate a raise, compare it with the latest annual CPI change. A 3% raise when prices rose 4% is a pay cut in real terms.
- When you set a savings goal years away, inflate today’s cost to the target year first.
- When you compare investments, look at the after-tax real return, not the headline rate.
For a quick check on how a raise compares with price growth, the percentage calculator shows the percentage change between two figures.
Why does your personal inflation rate differ from the CPI?
The CPI reflects an average basket. Your own spending may look very different. A renter in a city where rents are climbing fast, a retiree with heavy medical costs, or a long-distance commuter exposed to gas prices can face higher price growth than the headline figure, while a homeowner with a fixed-rate mortgage may face less. BLS publishes indexes for individual categories and for regions, so you can see which parts of your budget are rising fastest. Tracking your own spending for a year, and comparing it with the previous year, is the most accurate way to measure the inflation you actually experience.