Compound growth calculator
The eighth wonder of the world, with sliders. See what a starting amount plus a boring monthly habit turns into — and watch the growth line quietly lap the money you actually put in.
Educational tool, not advice. Real markets don't return a smooth X% a year — they lurch, crash, and recover their way to the average. Compounds monthly, ignores taxes and fees.
> time_in_market: doing its thing
| Year | Contributed | Balance | Growth |
|---|---|---|---|
| 2 | $22,000 | $24,339 | $2,339 |
| 4 | $34,000 | $40,825 | $6,825 |
| 6 | $46,000 | $59,782 | $13,782 |
| 8 | $58,000 | $81,578 | $23,578 |
| 10 | $70,000 | $106,639 | $36,639 |
| 12 | $82,000 | $135,455 | $53,455 |
| 14 | $94,000 | $168,587 | $74,587 |
| 16 | $106,000 | $206,683 | $100,683 |
| 18 | $118,000 | $250,486 | $132,486 |
| 20 | $130,000 | $300,851 | $170,851 |
// the two levers that matter most
Play with the inputs and you'll notice: early on, your contributions do the heavy lifting; late in the timeline, growth does nearly all of it. That crossover is the entire argument for starting early — the last ten years of a 30-year run typically create more money than the first twenty. Time is the input that can't be bought back later.
// what return should you assume?
The S&P 500's long-run average is roughly 10% before inflation, ~7% after. Using 7% keeps your projection in today's money, which is the honest way to plan. New to the underlying ideas? Read what is an index fund and what is dollar-cost averaging on the Press.