Content reviewed: 24 September 2026
How compound growth is calculated
Compound interest adds each period's interest to the balance, so later interest is earned on both the original principal and earlier interest. This calculator models a starting amount with a constant annual rate and a chosen compounding frequency.
Formula
P is the starting amount, r is the annual rate as a decimal, n is the number of compounding periods per year, and t is the number of years.
Example
If 10,000 grows at 8% per year compounded monthly for 10 years, the calculator applies one-twelfth of the annual rate 120 times. The result is a mathematical projection, not a promise of investment performance.
Important assumptions
The tool assumes the rate stays constant and that no money is added or withdrawn. It also excludes tax, fees, inflation and market volatility. If you plan to make regular deposits, use the Savings Goal Calculator for a contribution-based scenario.
See the Compound Interest Guide for an explanation of compounding frequency and the effect of time.