This calculator compounds a fixed monthly deposit at the rate you enter, year by year. It shows an estimated ending balance plus how much of that balance came from your own contributions versus growth. Real portfolios vary with market returns, taxes, employer matches, and sequence of returns.
Future value uses the end-of-month annuity formula on the monthly deposit with annual% ÷ 12 compounding each month. “Contributions only” is simply payment × number of months (no growth)—so the gap shows interest earned when rate > 0.
This calculator uses plain decimal numbers. If a result looks wrong, check whether you used a comma instead of a dot (or vice versa) where the field expects one.