Compound growth calculator

Enter a starting amount, a monthly contribution, and an annual return. Ask it either how long you need to hit a target, or what a fixed number of years gets you. All numbers are plain, in whatever currency you're thinking in.

Monthly compounding. No currency symbol: use the number in your own currency.

Starting amount in your currency Monthly contribution in your currency

Annual return % expected, before tax Target amount in your currency

Time to target

Total contributed

in your currency

Growth share

of final value, from returns

Monthly rate is derived from the annual return: (1 + annual) ^ (1/12) − 1. Each month the balance grows at that rate, then the contribution is added. "Years to target" runs that forward month by month until the balance clears the target, capped at 1200 months (100 years). "Value after N years" runs it forward a fixed number of months and reports where it lands.

Growth share is the part of the final balance that came from returns rather than from money you put in: (final − contributed) / final. It is the plainest way to see how much compounding, not saving, did the work.

This ignores fees, taxes, and sequence-of-returns risk: a single constant annual return smooths out a path that is never actually smooth. Treat the output as a rough planning number, not a forecast.

Personal record, not investment advice. No amounts, position sizes, or returns disclosed.