See how a starting amount plus regular contributions can grow over time. It's one of the most powerful ideas in personal finance, made concrete with your own numbers.
This tool runs a month-by-month simulation rather than a single formula, so it can handle any combination of contribution and compounding frequency correctly. Within each period, interest is applied to your existing balance first, and that period's contribution is added afterward, so new contributions start earning interest from the following period rather than immediately.
That timing detail is worth knowing about, since it's one of the small assumptions that can make one calculator's numbers differ slightly from another's for the same inputs. Whatever combination you choose above, the disclaimer beneath your results states exactly which assumption was used for that calculation.