Compound interest calculator

The eighth wonder of the world, Einstein supposedly said. See how your account grows over time and with contributions — and stay for the reality check on trading.

Your plan

ESTIMATED FINAL BALANCE
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Total balance What you put in
Total contributed
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Interest earned
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Why compounding is so powerful

Compound interest is earning interest on your interest. At first it feels slow and frustrating; over the years the curve takes off, because every dollar you earn starts generating its own dollars. That's why time and consistency (contributing a little, but always) matter more than chasing a jackpot.

⚠️ The reality check for traders. This calculator assumes a constant return, and that's the trap: in trading the return is NOT a fixed %. There are good months, bad months and drawdowns. An account that does +10% one month and −10% the next is not flat: it loses money (1.10 × 0.90 = 0.99). Volatility eats compounding. Anyone promising you "a guaranteed 10% monthly" is selling smoke — see how quickly an account really blows up in the risk of ruin calculator.

Use this tool for what it's actually good at: understanding the power of contributing consistently at a reasonable, sustainable return over the long run. Not to justify betting the account trying to double it in a month.

Frequently asked questions

What return is realistic?
Long term, broad stock indices have averaged roughly 6-9% a year (with red years). A consistent, good trader can beat that, but with volatility and no guarantees. Distrust any "fixed" double-digit monthly number.
How does the calculation compound?
Monthly: each month applies the proportional part of the annual return, then adds your contribution. It's a standard, conservative approximation for planning.
Is my data sent anywhere?
No. Everything is computed in your browser. No signup, no cookies, no server.

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Free educational tool. Not financial advice. Past returns do not guarantee future returns.