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Compound Interest Calculator

Compound Interest Calculator Separate the money you contribute from modeled growth, then see what the ending balance could buy in today's dollars.

Compound Interest Calculator estimate

Starting balanceMonthly contributionNominal annual return (%)Years

Advanced assumptions

Annual contributionContribution timingInterest compoundingAnnual inflation assumption (%)

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Your estimate

Enter values, then calculate.

How the estimate works

The nominal annual rate and selected compounding frequency determine an equivalent monthly growth rate. Monthly and annual deposits are then applied at the chosen beginning or end of each period. Purchasing power divides the ending balance by cumulative assumed inflation.
Change one assumption at a time to compare scenarios.
Use current balances, rates, costs, and timelines whenever possible.

Important limitation

This is an equivalent-rate projection, not a bank's exact daily-accrual convention. Annual deposits occur in the first or last month of each modeled year; monthly contributions are constant nominal dollars. No taxes, fees, changing returns or withdrawal policy are modeled. Results are estimates only and are not financial, lending, legal, tax, or investment advice.

Assumptions and review

Formula review: September 25, 2026. This tool uses only the values shown above and does not pull live rates, balances, prices, or account data.

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Frequently asked questions

What changes when I contribute at the beginning?

Each monthly deposit earns one extra month of growth, and each annual deposit is made at the beginning rather than the end of its modeled year. With a zero rate, timing makes no difference.

Is nominal return the same as APY?

No. The selected compounding turns a nominal rate into an effective annual rate. If your input is already an effective annual return, select annual compounding.

Does inflation change the account balance?

No. The nominal balance stays separate. The purchasing-power result discounts that balance to today's dollars using your constant inflation assumption.