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Compound Interest Calculator

Updated October 2026 Compound interest is interest on interest. Enter principal, rate, period and how often it compounds to see the effect — the gap between annual and monthly compounding widens sharply over long periods.
Compound Interest

Frequently Asked Questions

What is the compound interest formula?

A = P(1 + r/n)^(nt), where P is principal, r the annual rate, n the compounding frequency per year, and t the years.

How does compounding frequency change the result?

More frequent compounding produces a higher final amount for the same nominal rate, because interest starts earning interest sooner.

What is the rule of 72?

Divide 72 by the annual rate for a rough number of years to double your money. At 8%, roughly nine years.

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