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ToolsCompound growth calculator
Compounding is the whole argument for starting early, and it never feels true until you run your own numbers. Enter what you start with, what you add monthly, and an annual return, and see how much of the final figure is your money versus growth.
Final value
56,131
After 20 years of monthly compounding.
You put in
25,000
Growth added
31,131
Assumes a constant return with monthly compounding and contributions at each month's end. Real markets move unevenly — this shows the shape, not a promise.
How this calculator works
Compound growth means each year's returns start earning returns of their own. The calculator applies your expected annual rate, month by month, to a starting amount plus a fixed monthly contribution, and shows the final balance next to what you actually deposited. The gap between the two is compounding's work — small early, then increasingly not.
A worked example
Nothing to start, $100 every month, 7% average annual return, 20 years. You deposit $24,000; the balance ends near $52,100. Stretch it to 30 years and deposits of $36,000 end near $122,000 — the last decade alone contributes more growth than the first two combined. Time in, not timing, is doing the heavy lifting.
Common questions
- What return rate should I assume?
- Nobody knows the future — long historical averages for broad stock indexes sit near 7–10% a year before inflation, with brutal individual years inside that average. Run the tool at 5%, 7% and 9% and treat the range, not any single number, as the honest answer.
- Does the calculation account for inflation?
- No — the result is in future currency, which will buy less than today's. A rough real-terms view: subtract expected inflation from your return (7% growth at 3% inflation → run it at 4%). The inflation-impact tool next door shows what that erosion looks like on its own.
- Monthly contributions or a lump sum — which grows more?
- Mathematically, money invested earlier compounds longer, so an early lump sum ends higher than the same total dripped in. But most people don't have the lump sum — they have a salary. Steady contributions are how the compounding actually happens; the DCA article covers why the habit also removes timing stress.
What this tool can't tell you
A smooth 7% is a fiction that real markets never deliver — actual sequences include crashes, and a bad early decade changes the picture. The tool also ignores fees and taxes (the fund-fee tool prices the former). It shows the shape of compounding, not a promise of it.
These tools are for education. They work from the numbers you type and cannot see your accounts, verify who owns an address, or account for your circumstances. Nothing here is financial advice.