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Compound Interest Calculator

See how your money grows with compound interest. Model different rates, contribution schedules, and time horizons — and see the impact of inflation on your real purchasing power.

Starting amount (USD)

Annual return (%)

Time horizon (years)

Compound frequency

Regular contribution (USD)

Contribution frequency

Annual inflation rate (%) — optional

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Final balance after — years

Total contributions

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Interest earned

—

Inflation-adjusted

—

Real interest earned

—

Year-by-year breakdown

Year	Balance	Contributed	Interest	Real value

Inflation-adjusted values use the Consumer Price Index (CPI) model — they show what the future balance is worth in today's dollars. Real interest is the nominal return minus inflation. These are projections, not guarantees. Past performance does not predict future returns.

How compound interest works

Compound interest means you earn interest on your interest, not just your principal. Over long time horizons this creates exponential rather than linear growth. Albert Einstein allegedly called it the eighth wonder of the world — whether or not he said it, the mathematics are undeniable: at 7% annual return, your money doubles roughly every 10 years.

The inflation adjustment converts nominal returns (what you see in the account) to real returns (what you can actually buy). At 7% return and 3% inflation, your real annual return is approximately 4%, and your balance after 20 years is worth significantly less in today's purchasing power than the nominal figure suggests.

How to verify this calculator

Last verified: 8 November 2026 — the calculation logic and the automated regression suite were re-run on this date. Fee and rate fields are editable estimates; confirm current values against the official schedule before relying on them.
Official / methodology source: Federal Reserve — policy interest rates — confirmed reachable on 2026-11-08.
Method & testing: All arithmetic runs locally in your browser — no input is uploaded. Calculation behaviour is exercised by the repository's regression suite: 39/39 checks passed (run 2026-11-08). Source & tests on GitHub.
Maintained by: Jim (Maoming, Guangdong, China) · eyetoolkit. Report a wrong result through the contact page.
Changelog: 2026-11-08 — Added this verification panel (last verified date, official or methodology source, test coverage, named maintainer, changelog). Calculator logic and default rates are unchanged.