Compound interest calculator
Shows how a deposit grows when profit stays in play: per trade, day, week or month — plus a savings mode with an annual rate and compounding, the way a bank counts it.
Final amount
$589.16
Net profit
+$489.16
Total invested
$100.00
Growth on invested
×5.89
How many times the invested amount grew
Balance curve
How the amount grows
| Period | Balance | Invested | Profit |
|---|---|---|---|
| Day 5 | $115.93 | $100.00 | +$15.93 |
| Day 10 | $134.39 | $100.00 | +$34.39 |
| Day 15 | $155.80 | $100.00 | +$55.80 |
| Day 20 | $180.61 | $100.00 | +$80.61 |
| Day 25 | $209.38 | $100.00 | +$109.38 |
| Day 30 | $242.73 | $100.00 | +$142.73 |
| Day 35 | $281.39 | $100.00 | +$181.39 |
| Day 40 | $326.20 | $100.00 | +$226.20 |
| Day 45 | $378.16 | $100.00 | +$278.16 |
| Day 50 | $438.39 | $100.00 | +$338.39 |
| Day 55 | $508.21 | $100.00 | +$408.21 |
| Day 60 | $589.16 | $100.00 | +$489.16 |
The calculation shows the math of compound interest at a constant return. In real trading the return fluctuates and runs of losses break the curve — treat the result as a reference point, not a forecast.
How compound interest works
Compound interest means profit is credited not only on the starting amount but also on what has already been earned. Every next period begins with a bigger deposit, so the same percentage return brings progressively more money.
The formula does not change whether you are counting a trading account or a deposit:
Final = starting amount × (1 + return per period) ^ number of periods
The calculator runs that formula and adds what the bare formula leaves out: top-ups (credited at the end of each period, earning interest from the next one) and a period-by-period breakdown — so you see the whole path, not just the endpoint.
Two modes for two different questions
Trading. The return is set per period, and you pick the period: trade, day, week, month or year. That keeps the numbers in familiar terms — “2% a day”, “5% a week”.
Savings. Here the rate is annual and compounding is daily, monthly, quarterly or yearly. This is how banks count, which is why the results include an effective rate: 16% a year compounded monthly actually yields 17.23%. The gap between the advertised and the effective rate is exactly what compounding contributes.
A worked example
Deposit $100, return 3% a day, 60 trading days — about three working months.
| Accrual method | Final | Profit |
|---|---|---|
| Simple interest ($3 a day) | $280 | $180 |
| Compound interest | $589 | $489 |
Same return, same term — the $309 difference appeared only because profit stayed in play. That is the whole effect of compounding: it does not raise your return, it stops that return from sitting idle.
Where the calculations go wrong
- Overstating the return per period. The most common mistake. Sanity-check it over a long horizon: if a year out the number is one you would not believe yourself, the rate is unrealistic.
- Counting without drawdowns. One losing month throws the curve back several periods, and growth then continues from a smaller base. It helps to run two scenarios — a base case and one with two or three bad periods.
- Forgetting withdrawals. Compounding only works on the part of the profit that stays in the account. Withdraw half of what you earn regularly and the real curve sits well below the calculated one.
- Confusing deposit growth with win rate. These are different things: a deposit can grow at a 55% win rate and shrink at 65% if the trade sizes differ.
FAQ
How is compound interest different from simple interest?
Simple interest always counts profit from the same starting amount, compound interest counts it from the grown deposit. Over a short run the gap is barely visible, over a long one it decides everything: 3% a day on $100 produces $180 of profit in 60 days with simple interest and $489 with compound.
What return per period is realistic to assume?
A smaller one than you would like. Sanity-check the figure by running it forward: 5% a day over 250 trading days turns $100 into roughly $19.8 million — a result that refutes itself. For planning, 1–2% a day is saner, with idle stretches and drawdowns budgeted separately.
Can I use it for a bank deposit?
Yes, that is what the Deposit mode is for: you set the annual rate, the term and the compounding frequency, and the calculator returns the final amount and the effective rate. It works in your deposit currency — substitute dollars, euros or rubles, the formula is identical.
Are taxes and fees included?
No. The calculator shows the pure math of the accrual. Tax, withdrawal fees or account maintenance charges have to be subtracted from the result yourself.