Enter what you have, what you're adding each month, the return you expect, and how long you'll leave it. See exactly when compounding starts pulling ahead of your contributions.
A $10,000 starting balance plus $500/month at 7% for 30 years grows to roughly $640,000 — about $460,000 of which is compound growth, not contributions.
The "rule of 72" gives a quick estimate: divide 72 by your annual return rate to see roughly how many years it takes for your money to double. At 7%, that is roughly 10 years.
Compound interest is interest earned on interest. Each period, your balance grows by the previous balance times the periodic rate, then your contribution is added. Over decades the compounded portion dwarfs the contributed portion — the "hockey stick" curve every personal-finance article keeps showing you.
P is your starting amount. PMT is each monthly contribution. r is the monthly rate (annual ÷ 12). n is the total number of months. Each input above is plugged into this formula and the chart shows the running balance year by year.
Important: figures are nominal — they don't subtract inflation, fees, or taxes. To see "real" growth, subtract roughly 2–3% from your return assumption to net out inflation.
Compound interest is interest earned on both your original deposit AND on the interest already credited. It causes balances to grow faster over time — the longer you leave money invested, the more dramatic the effect.
Future Value = Principal × (1 + r)n + PMT × ((1 + r)n − 1) / r, where r is the periodic interest rate (annual rate ÷ 12 for monthly compounding) and n is the total number of periods.
For a globally-diversified equity index fund, 6–8% annualised is a common historical assumption. Cash and bonds run lower. This calculator does not promise any specific return — model multiple scenarios.
No — the figures shown are nominal. To see real (after-inflation) growth, subtract an inflation estimate (typically 2–3%) from your assumed return rate before entering it.
No. If you're saving inside a tax-advantaged retirement account, returns are typically tax-free or tax-deferred. Outside one, capital gains and dividend taxes will reduce the effective return.
ProFinanceCast turns one-off calculations into a living 10-year forecast that updates as your income, expenses, and goals change. Free forever for the core forecast.