Quiet Zeros

Calculators / Saving & investing

Compound interest

The eighth wonder, charted: what a starting balance plus steady contributions becomes over time. Nothing you type leaves this page.

$

Enter $0 to $50,000,000.

$

Enter $0 to $1,000,000.

%

The S&P 500 has averaged ~10% before inflation, ~7% after.

Enter 0 to 30%.

yrs

Enter 1 to 60 years.

Balance after __YEARS__

—

You contributed

—

Growth earned

—

Multiple of contributions

—

Contributions vs. growth over time

Year-by-year table

How this is calculated

Interest compounds monthly: each month the balance earns one-twelfth of the annual return, then your contribution is added.

balancem+1 = balancem × (1 + r/12) + contribution

The chart splits the result into two honest layers: money you put in, and money the money made. Early on, contributions dominate. Given enough years the growth layer overtakes them — that crossover is the whole argument for starting early.

Choosing a return

Nobody knows future returns. A common planning range for diversified stock portfolios is 5–8% after inflation; savings accounts track prevailing rates. Try a pessimistic and an optimistic number and plan between them.

Notes

Returns are assumed steady, which real markets never are, and taxes and fees are ignored — both drag on the result. Treat this as a planning envelope, not a forecast.

Related tools