Compound Interest With Inflation Calculator
Every projection has two numbers: the one on the statement, and the one that matters. This calculator shows both — your nominal balance and what it will actually buy, in today's dollars.
Your inputs
Nominal vs real, year by year
Year-by-year breakdown
| Year | Nominal balance | In today's dollars | Inflation's cut |
|---|
Nominal growth vs real growth
Your account balance grows at the nominal rate — that's real money, and it really will be in your account. But prices grow too. If your money compounds at 8% while prices compound at 3%, your purchasing power only grows at the real rate — about 4.85% a year. The exact relationship is the Fisher equation:
Today's dollars = nominal balance ÷ (1 + inflation)years
The quick approximation "nominal minus inflation" (8% − 3% = 5%) is close, but slightly optimistic — over decades the small gap between 5% and 4.85% compounds into real money, so this calculator uses the exact formula. Our main compound interest calculator shows the same plan without the inflation lens; comparing the two is the fastest way to feel how much of the headline growth is real.
Worked example
Start with $10,000, add $500/month, earn 8% nominal with 3% inflation for 25 years. The nominal balance reaches $548,915. Sounds great — until you deflate it: in today's dollars that pile buys what $262,165 buys now. Inflation quietly took $286,750 — more than half the headline number, and more than the $160,000 you contributed out of pocket. Your true compounding rate was never 8%; in purchasing-power terms it was 4.85%.
Why this changes decisions
Goals live in today's dollars: the house, the retirement budget, the college bill as you'd price them now. If you save toward a $500,000 goal "in 25 years" using nominal math, you'll arrive with $500,000 that spends like roughly $239,000 — and wonder what went wrong. Planning in real terms fixes the target: either save more, start earlier, or accept a genuinely lower goal. It also reframes cash: money earning less than inflation isn't "safe", it's a guaranteed slow loss — at 0% interest and 3% inflation, $10,000 of purchasing power becomes about $4,800 over 25 years.
Caveats worth knowing
- Inflation isn't constant. It averaged roughly 3% over the very long run in the U.S., but individual decades ran far hotter (the 1970s) and cooler (the 2010s). Try 2% and 5% to see the range of outcomes.
- Your personal inflation differs. Housing, healthcare, and college costs have often risen faster than headline CPI; renters and homeowners experience different inflation.
- Taxes are charged on nominal gains. In a taxable account you owe tax on the full nominal gain — including the part that merely kept up with inflation — which lowers your after-tax real return further.
- Returns aren't smooth. The nominal rate here is a steady hypothetical average; real markets arrive in lumps.
Sources: U.S. Securities and Exchange Commission, compound interest calculator and explainer (investor.gov); the real-return formula is the standard Fisher relation.