Compound Interest Calculator
Updated July 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.