Compound Interest Calculator

Compound interest is what makes long-term savings and investments grow faster than simple interest ever could, because each period's interest is calculated on the principal plus every bit of interest already earned, not just the original amount. This calculator takes a principal, an annual interest rate, a length of time in years, and a compounding frequency, and shows both the final amount and exactly how the balance builds up year by year.

The formula behind it is A = P × (1 + r/n)ⁿᵗ, where A is the final amount, P is the principal, r is the annual interest rate (as a decimal), n is the number of times interest compounds per year, and t is the time in years. Switching the compounding frequency between annually (n = 1), monthly (n = 12), and daily (n = 365) changes how often that interest gets folded back into the balance: the more frequently interest compounds, the faster the balance grows for the same nominal annual rate, since each compounding period's interest starts earning its own interest sooner.

Beyond the final total, this tool builds a full year-by-year growth table showing the starting balance, interest earned, and ending balance for every year of the term, so you can see exactly how much of the final amount came from the principal versus from compounding itself, useful for understanding why a long-term investment's growth curve bends upward over time rather than climbing in a straight line the way simple interest would.

Every figure and every row of the table updates live as you type or change the compounding frequency, with no "Calculate" button to press. Every calculation runs as plain JavaScript directly in your browser, so nothing you type is ever sent to a server, logged, or stored anywhere.