Compound growth calculator
Put in a starting balance, what you add each month, and how long you leave it. The split at the bottom is the part most people find surprising.
After 30 years
$618,102
You put in
$181,000
Growth
$437,102
71% of the final balance
Year by year
| Year | Contributed | Balance | Growth |
|---|---|---|---|
| 5 | $31,000 | $37,214 | $6,214 |
| 10 | $61,000 | $88,552 | $27,552 |
| 15 | $91,000 | $161,330 | $70,330 |
| 20 | $121,000 | $264,502 | $143,502 |
| 25 | $151,000 | $410,761 | $259,761 |
| 30 | $181,000 | $618,102 | $437,102 |
How this is calculated
The starting balance grows at the annual return you enter, compounded monthly. Each monthly contribution is added at the end of its month and compounds from there — so a contribution made in year one has far longer to grow than one made in year twenty.
The formula, where r is the monthly rate and n the number of months:
future value = P × (1 + r)ⁿ + PMT × ((1 + r)ⁿ − 1) ÷ rWhat the result does and does not tell you
A single average return hides how markets actually behave. Real returns arrive unevenly — a run of bad years early on leaves you worse off than the same average arriving in a different order, even though this calculator would show both as identical. Treat the output as the shape of compounding, not a forecast.
It also ignores inflation, fees, and taxes. A 7% return with 3% inflation is closer to 4% in purchasing power, and a fund charging 1% a year takes a meaningful bite out of a multi-decade balance. If you want the number in today’s money, enter a return already reduced by expected inflation.
Educational only. This explains how these products and accounts work in general. It is not financial, tax, or legal advice, and not a recommendation to buy anything. Your situation is specific to you — check with a licensed professional before acting.