Compound Interest Calculator — Free Online Tool

The Compound Interest Calculator projects how a balance grows when returns are earned on previous returns as well as on the original principal, taking your starting amount, regular contributions, expected rate, compounding frequency, and time horizon.

Compounding is non-linear, and that is the whole point. The growth curve is nearly flat for years and then bends upward sharply, which means the outcome is far more sensitive to time than to the amount contributed. A smaller sum invested early routinely beats a larger sum invested later, and the gap widens the longer the horizon — this is the single most important fact in personal finance and the least intuitive.

Compounding frequency matters less than people assume. Moving from annual to monthly compounding at the same nominal rate adds a modest amount; moving from monthly to daily adds very little. The rate and the number of years dominate everything else.

Two honesty checks on any projection. First, it assumes a constant rate, and real markets do not deliver one — a 7 percent average across twenty years arrives as a sequence of good and bad years, and the order of those years affects the outcome if you are withdrawing. Second, the figure is nominal. At 3 percent inflation, money roughly halves in purchasing power over 24 years, so a projection that looks large in future currency is worth meaningfully less in today's terms. Subtracting inflation from your assumed rate gives a more honest picture.

Calculation runs entirely in your browser.

Our Compound Interest Calculator is completely free to use with no signup required. For this tool, processing runs in your browser — your files and data stay on your device and are not uploaded to our servers.

Whether you are a developer, designer, student, or business owner, this tool is designed to save you time and make your workflow more efficient. Bookmark this page to access it whenever you need it — it will always be free.