Compound Interest Calculator

The engine steps through your investment one month at a time. Each month it applies a slice of whichever compounding schedule you picked, worked out as (1 + r/n) raised to the power of n divided by 12. With no deposits, that produces exactly the same answer as the standard A = P(1 + r/n)^(nt) formula, so a lump sum at 7% compounded daily gives the same number here as it does in a textbook.

Monthly stepping matters once regular deposits are involved. A quarterly deposit lands in months 3, 6, 9, and 12 rather than being smeared evenly across the year, and the start-of-period option gives every deposit one extra month of growth before interest is applied. That gap is barely visible in year one and clear by year twenty.

The year-by-year table is built while the simulation runs, so each row shows the real balance at that point instead of a figure worked backwards from the total. The bar under the headline splits the final balance three ways: what you started with, what you paid in, and what the interest produced. Watching that third band overtake the other two shows why time in the market matters more than any single deposit.

The inflation field divides the final balance by (1 + inflation)^years to show today's buying power. Tax and fees are not modelled, because both depend on your country and account type. For a rough allowance, subtract your yearly fee from the interest rate before entering it.