Interest Calculator
Grow a lump sum with compound interest.
About the Interest Calculator
See what a lump sum grows to with compound interest. Enter your starting amount, annual interest rate, the number of years, and how often it compounds per year — the calculator returns the ending balance and the interest earned. It's the fundamental savings and investment calculation, and adjusting the compounding frequency shows why 'compounded monthly' beats 'compounded annually' at the same rate.
How to use the Interest Calculator
- 1Enter your starting amount, interest rate, years, and compounds per year.
- 2Read the result instantly — it recalculates as you type.
- 3Adjust the numbers to model different scenarios.
Frequently asked questions
What is compound interest?
Interest earned on both your original principal and the interest already added — which is why balances grow faster the longer they're left to compound.
Does compounding frequency matter?
Yes — more frequent compounding (monthly vs annually) yields slightly more at the same nominal rate. The gap widens over long periods.
How is this different from simple interest?
Simple interest is calculated only on the principal. Use the Simple Interest Calculator for that; this one compounds.