Compound Interest Calculator
See how investments grow over time. Visualize compound growth with a chart and yearly table.
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When to use this
You want to know what happens if you invest $500/month for 25 years. Or you're trying to show a teenager why starting a Roth IRA at 18 instead of 30 means retiring with twice the money despite contributing less. Compound interest is the single most important concept in personal finance, and this calculator makes it visual.
It's also the tool that settles debates. "Should I invest a lump sum or dollar-cost average?" "Does compounding frequency actually matter?" "How much does a 1% fee drag on returns over 30 years?" Plug in the numbers and see for yourself — the chart makes the answer obvious in a way that formulas don't.
The growth chart is the key feature. Watching the gap widen between your contributions (the money you put in) and your total balance (what compounding grew it to) is the most powerful financial visualization there is.
Good to know
Starting early beats investing more. $200/month from age 22 to 65 at 8% grows to ~$940,000. $400/month from age 32 to 65 (same total contributed: ~$158,000 vs ~$103,000) grows to only ~$680,000. The 10 extra years of compounding are worth more than doubling your contribution.
Compounding frequency barely matters. Monthly vs. daily vs. continuous compounding on a $10,000 investment at 7% over 30 years differs by less than $500. Don't let anyone sell you a product based on "daily compounding" — the edge is trivial.
The Rule of 72 is your mental shortcut. Divide 72 by the annual return rate to estimate how many years it takes to double your money. At 8%, money doubles every 9 years. At 6%, every 12 years. At 10%, every 7.2 years.
Fees compound too — in reverse. A 1% annual fee doesn't sound like much, but on a $500,000 portfolio over 30 years at 8%, it costs you roughly $300,000 in lost growth. Compound interest giveth, and compound fees taketh away.
Quick Reference
| Monthly Investment | Years | Return | Total Contributed | Final Balance |
|---|---|---|---|---|
| $200 | 10 | 8% | $24,000 | $36,589 |
| $200 | 20 | 8% | $48,000 | $117,804 |
| $200 | 30 | 8% | $72,000 | $298,072 |
| $500 | 20 | 7% | $120,000 | $260,464 |
| $500 | 30 | 7% | $180,000 | $610,729 |
| $1,000 | 30 | 8% | $360,000 | $1,490,359 |