Start with a balance, add a monthly contribution, set the rate — and watch the curve bend. Year-by-year table, savings-goal planner, and a compound-vs-simple comparison that makes the point better than any lecture.
Constant rate, contributions every month, no withdrawals, taxes ignored. Real investing varies — compounding maths doesn't.
Work it backwards: pick a target and we'll show how long your current plan takes to hit it — or what monthly contribution gets you there on your schedule.
Same money, same rate, same time. Simple interest earns on the principal; compound interest earns on the principal and every dollar it already earned.
The full schedule for the plan above — contributions in, interest earned, and where the balance ends each year.
| Year | Contributed | Interest this year | Total interest | Balance |
|---|
Every figure comes from closed-form compound interest maths — here's exactly what's applied.
A = P(1 + r/n)nt, where P is the starting balance, r the annual rate, n the compounding periods per year, and t the years. Daily compounding at the same nominal rate always beats monthly, which beats annually.
Contributions use the effective rate for the contribution period (monthly), so the "Compounding" setting still decides the true growth. The future-value-of-an-annuity formula sums every deposit's own growth period; start-of-month deposits each earn one extra period.
Solved with logarithms where possible: n = ln(1 + i·FV/PMT) / ln(1+i), i being the monthly effective rate. If your goal needs a negative monthly amount (the start balance already overshoots with zero contributions), we flag it.
Taxes, fees, inflation, changing returns and contribution increases. A real portfolio is volatile; the honest version of this tool is a constant-rate projection, clearly labelled as one.