Compound Interest Calculator

A compound interest calculator shows how an amount of money grows over time when the interest you earn is added back to the balance and then earns interest of its own. Enter your starting principal, the annual interest rate, the number of years and how often interest compounds each year, and this calculator instantly shows your final amount and the total interest earned.

Compound interest is interest on interest. Unlike simple interest, which is calculated only on the original principal, compound interest is calculated on the principal plus all the interest that has already accrued. The more frequently interest compounds — yearly, monthly or daily — the faster the balance grows, because each new interest payment immediately starts earning more. The growth follows the formula A = 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 number of years.

Use it to project savings accounts, fixed deposits, bonds or long-term investments, or to compare how rate, time and compounding frequency change your returns. Small differences compound dramatically over decades, so try lengthening the time horizon or raising the frequency to see the effect. Everything is calculated in your browser — no figures are uploaded, logged or stored anywhere.