Compound Interest with Monthly Deposits Calculator

About this calculator

This calculator combines two growth streams: compound interest on the starting balance, FV₁ = P × (1 + r/12)^(12t), and a stream of monthly contributions, FV₂ = PMT × [((1 + r/12)^(12t) − 1) / (r/12)] — the future value of an ordinary annuity. Adding them gives the total ending balance, from which subtracting your original balance and total deposits isolates the interest actually earned.

It's the calculation behind "pay yourself first" savings plans and retirement projections, letting savers see concretely how a modest but consistent monthly deposit — $200 a month, say — compounds into a much larger sum than the deposits alone would add up to, especially over a decade or more.