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
Total balance What you put in
Total contributed
Interest earned

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.