Investment Growth Calculator
See how a starting balance and steady monthly contributions compound over time — and, the eye-opening part, how much of your ending balance is growth versus money you actually put in.
After 30 years
$252,111
$179,111 of that is growth — 71% of the ending balance.
Assumes a fixed annual return compounding monthly with contributions made at month-end. Real markets are volatile and returns are not guaranteed; this is an illustration, not a forecast or financial advice. How we work.
Worked examples
Straight from the calculator, at a conservative 6–8% return. Notice how the growth column overtakes what you put in as the horizon stretches.
| Scenario | Ends at | You put in | Growth |
|---|---|---|---|
| $1,000 · $200/mo · 7% · 30 yr | $252,111 | $73,000 | $179,111 |
| $0 · $500/mo · 8% · 25 yr | $475,513 | $150,000 | $325,513 |
| $10,000 · $100/mo · 6% · 20 yr | $79,306 | $34,000 | $45,306 |
| $5,000 · $300/mo · 7% · 40 yr | $869,001 | $149,000 | $720,001 |
In the 40-year row, more than four out of every five dollars came from growth, not contributions. That gap is the whole argument for starting early.
How to read your result
Two levers move the ending number more than anything else: time and how much you add each month. Because each year's growth compounds on top of the last, the curve bends upward — so an extra five or ten years at the end is worth far more than the same span at the start. Try nudging the years field up by five and watch the growth figure jump.
Be honest with the return rate, though. The number here is a smooth line; real markets are not. A broad index has historically averaged high-single-digits after inflation over long stretches, but it gets there through gut-churning up and down years, and no return is guaranteed. Use a conservative rate, treat the output as an illustration rather than a promise, and remember it's a pre-tax, pre-inflation figure.
Where the money actually goes is your decision. For hands-off, long-horizon investing we've used both a brokerage and a real-estate platform ourselves — the honest trade-offs are in our Robinhood review and our Fundrise review.
FAQ
What return rate should I use?
Be conservative. A common long-run benchmark for a broad US stock index is about 10% nominal, or roughly 7% after inflation — but any single year can be sharply up or down, and past performance doesn't guarantee future results. Bonds and cash return less. If you want a realistic picture in today's dollars, use a real return like 6–7% rather than a rosy 12%.
Does this account for inflation or taxes?
No — the result is a nominal, pre-tax figure. To approximate today's purchasing power, subtract expected inflation from your return (e.g., 7% nominal minus 3% inflation ≈ 4% real) and run it again. Taxes depend on the account: a Roth IRA grows tax-free, a taxable brokerage does not.
Why is the ending number bigger than a simple interest calculation?
Compounding. Each period's growth earns its own growth the next period, so the curve bends upward over time — which is why starting early matters more than the exact rate. The longer the horizon, the larger the share of the ending balance that is growth rather than money you contributed.
Monthly or annual compounding?
This tool compounds monthly and assumes contributions are made at month-end, which matches how most people actually invest (every paycheck). Calculators that compound annually will show slightly different totals — the gap is small over long horizons.
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Estimates assume a fixed annual return compounding monthly, with contributions at month-end. Real returns are variable and not guaranteed, and figures are pre-tax and pre-inflation. This is an illustration, not financial advice.