Educational tool only — not financial advice. Projected returns are assumptions, not promises — real balances move with markets, fees, and timing. Confirm your own figures against your statements before acting on them.
How to use this calculator
Enter a value in each labelled field above. The defaults are sensible starting points, so you can see a complete result immediately and then adjust any single input. The tool recalculates on every keystroke, so the result cards always reflect your latest numbers — there is nothing to submit, no account to create, and no data is sent anywhere.
- Set the starting bankroll. The initial deposit is the capital that compounds from day one — treat it as the balance you have dedicated to the account, not your net worth.
- Model your funding schedule. The monthly contribution is what you add on a regular basis. A negative value works too: use it to draw the account down over time, the mirror image of the accumulation phase.
- Enter a return you can defend. The annual rate is divided by twelve and applied monthly — the same nominal convention an APR uses. If you track your own monthly percentage, convert it first by multiplying by twelve: a steady 2% a month is entered as 24%.
- Stretch the horizon. Time is the strongest lever in the formula. Extend the years and watch the interest-earned card close the gap on total contributed — the crossover is where compounding starts doing the heavy lifting.
How this calculator works
The result you see is produced by a short formula that runs directly in your browser using the values you entered. There is no server round-trip: your inputs never leave this page, nothing is logged or stored, and the tool keeps working offline once the page has loaded. The formula itself is published in the page source, so anyone can audit exactly how each output is derived.
The math itself is monthly compounding with a regular contribution. Each month the balance earns one twelfth of the annual rate, then the contribution lands on top: balance = balance × (1 + annual rate ÷ 12) + contribution, repeated for every month in the horizon. Final balance is the ending value of that loop, total contributed is the initial deposit plus every contribution, and interest earned is the gap between the two. Over long horizons the interest component grows faster than the contributions — the curve steepens each year instead of climbing in a straight line, which is exactly the effect this calculator is built to expose.
Why traders should model compounding
Compounding is the reason a steady plan beats one spectacular year. Two levers drive the curve: the return you assume and the contributions you keep adding. Raise the rate and the curve steepens; raise the contribution and the base grows faster. Change one field in the calculator above at a time — the gap between final balance and interest earned shows which lever actually moved the ending number further.
The rule of 72 is a quick sanity check: divide 72 by the annual return to get the approximate doubling time. At 10% a year, money roughly doubles every seven years, so the $10,000 default on this page compounds to about $27,000 in ten years with no contributions at all. Add $200 a month and the same account finishes near $68,000 — contributions and interest earning on each other the whole way.
Drawdowns are the other half of the story, and this is where the compounding math catches traders out. A 20% loss needs a 25% gain to break even; a 50% loss needs 100%. The curve only keeps its shape if the losing stretch stays survivable, so pair this calculator with the sizing tools: work out stake size with the position size calculator and see how a string of losses bends the curve with the risk of ruin calculator.
Treat the return field as an assumption, not a promise. Run the projection twice: once at the rate you hope for and once at something boring. If the boring case still reaches the goal, the plan is not hanging on a single lucky assumption.
Methodology and limitations
Every figure produced here is an estimate intended for planning and education. Markets do not deliver a steady rate: returns arrive unevenly, fees and taxes take a cut, and inflation reduces what the ending balance will actually buy. A contribution schedule you cannot maintain breaks the projection just as surely as a lower return would. Treat every output as a scenario rather than a forecast, and check it against your own statements before making decisions. This page does not constitute investment, tax, or financial advice.
Compounding turns steady contributions into the majority of your ending balance over long horizons. Model your own schedule here — and remember that projected returns are assumptions, not guarantees.
Frequently Asked Questions
What return should I assume?
Historical long-run equity averages sit around 7-10% before inflation; using a conservative 5-8% keeps the projection honest.
Is compounding monthly realistic?
Yes for accounts that reinvest dividends and gains monthly - the calculator compounds monthly to match.
Are trading returns compoundable like this?
Only if you reinvest profits and avoid large drawdowns - a single -50% year needs a +100% year just to break even.