How to Use the Compound Interest Calculator
Enter a starting balance (or zero), an expected annual interest rate, how often it compounds, any regular contribution amount, and the number of years — the calculator projects the future balance and typically breaks down how much came from contributions versus how much came from compound growth itself.
The Compound Interest Calculator handles the full growth projection — here's what each input controls and how to read the breakdown it produces.
The core inputs
Starting balance, annual interest rate, compounding frequency, and time horizon in years form the base projection. Adding a regular contribution amount (monthly is most common) layers ongoing growth on top of the initial balance, matching how most real savings and investment accounts actually work.
Reading the contributions-vs-growth breakdown
Beyond the final total, the calculator typically separates how much of the final balance came from money actually contributed versus how much came purely from compound growth — a useful way to see how much of a large final number is "your money" versus growth on top of it.