Compound Interest Calculator

Interest that earns interest. Compare compounding with simple interest and see how much time matters.

Final amount

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Total put in

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Interest earned

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With simple interest

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The rule of 72

Divide 72 by the interest rate to estimate how many years it takes to double your money. At 8%, that's about 9 years; at 12%, about 6. Compounding is slow at first and dramatic later, which is why starting early matters more than starting big.