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Compound Interest Calculator

Calculate compound interest growth over time. Enter principal, rate, frequency and years to see your final balance and total interest earned. Supports monthly, quarterly or annual compounding.

The Compound Interest Calculator is a free online tool. Enter your principal, annual interest rate, compounding frequency and investment period to see exactly how your money grows. Shows final balance and total interest earned side by side.
Compound Interest

How to use

1

The Rule of 72

Divide 72 by your annual interest rate to find how many years it takes to double your money. At 7%, money doubles every ~10 years. At 10%, every ~7 years.

2

Compounding frequency

Monthly compounding gives slightly more than annual. On £10,000 at 7% over 20 years: annually gives £38,697; monthly gives £40,096 — about £1,400 extra, for free.

💡 Did you know?

Albert Einstein reportedly called compound interest the 'eighth wonder of the world', though historians dispute whether he actually said it. What's not disputed: £1 invested in 1800 at 7% compound annual growth would be worth over £100 million today.

Reviewed for 2026. Built by a UK-based qualified primary teacher and FA Level 2 coach as part of 247QuickTools' free utility-tools project.