Compound Interest Calculator
See the power of compound interest on your savings and investments. Add regular contributions to see how small monthly amounts grow dramatically over time.
How compound interest works
Compound interest means you earn interest on your interest. Unlike simple interest (where you only earn on the original principal), compound interest adds earned interest back to your balance — and then earns interest on that larger balance in the next period.
The more frequently interest compounds, the faster your money grows. Daily compounding grows slightly faster than monthly, which grows faster than annual compounding.
The rule of 72
A quick way to estimate how long it takes to double your money: divide 72 by your annual interest rate. At 6% interest, your money doubles in approximately 72 ÷ 6 = 12 years. At 9%, it doubles in 8 years. This rule works for any compounding investment.