Compound Mint

How compound interest actually works

3 numbers decide it. One of them matters most.

Educational content only. Not financial advice.

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1. The amount

$200 a month for 30 years at 8% grows to about $298,000. $400 a month: about $596,000.

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2. The return

Same $200 a month for 30 years. At 4%: about $139,000. At 8%: about $298,000.

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3. The years

$200 a month at 8%. Time does the heavy lifting.

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The last 10 years win

Years 30 to 40 add about $400,000. That is more than the first 30 years combined.

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The rule of 72

Divide 72 by your return to get the years to double. 8%: 9 years. 10%: about 7. 2%: 36.

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Run your own numbers

Try the free compound interest calculator in the full guide.

Educational content only. Not financial advice. Examples are hypothetical, not guaranteed.