Free Compound Interest Calculator
Work out how a principal grows with compounding interest — no signup, nothing sent to a server.
Total amount
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Compound interest
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How to calculate compound interest
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1
Enter the principal amount
Type the original sum being invested or borrowed.
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2
Enter the annual interest rate
Use the nominal annual rate quoted for the account or loan.
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3
Set the time period
Enter the number of years the amount will compound for.
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4
Pick a compounding frequency
Choose annually, semi-annually, quarterly, or monthly.
Example use cases
Savings & fixed deposits
Estimate how a lump-sum deposit grows under a given compounding schedule.
Comparing accounts
Compare the effect of different compounding frequencies at the same nominal rate.
Long-term growth projections
See how principal compounds over multi-year horizons before committing funds.
Frequently asked questions
How is compound interest calculated?
Total amount = P × (1 + r/n)^(n×t), where P is the principal, r is the annual rate as a decimal, n is the number of times interest compounds per year, and t is the time in years. Compound interest is the total amount minus the principal.
How is compound interest different from simple interest?
Simple interest is calculated only on the original principal each period. Compound interest is calculated on the principal plus interest already accumulated, so growth accelerates over time. See the Simple Interest Calculator for that version.
Does compounding frequency really make a difference?
Yes — more frequent compounding (monthly vs. annually) produces a slightly higher final amount for the same nominal rate, since interest starts earning interest sooner.
Is my financial information sent to a server?
No. The calculation runs entirely in your browser — nothing is transmitted or logged.