Compound Interest Calculator
See how your investment grows exponentially over time.
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12550 yrs
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Final Balance
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Contributed
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Principal + deposits
Interest Earned
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Growth Over Time
Year-by-Year Breakdown
| Year | Balance | Contributed | Interest | Return |
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What is Compound Interest?
Compound interest earns interest on both your principal and previously earned interest — making your money grow exponentially. Einstein reportedly called it the "eighth wonder of the world."
A = P × (1 + r/n)^(nt) + PMT × [((1 + r/n)^(nt) − 1) / (r/n)]
What annual return should I use?
The S&P 500 has historically returned ~10% nominally or ~7% inflation-adjusted. Use 7% for a conservative long-term stock market estimate.
How does compounding frequency affect growth?
More frequent compounding yields slightly more. Daily vs. monthly makes a small difference in practice, but monthly vs. annual can be meaningful over decades.
Should I include monthly contributions?
Absolutely. Even small regular contributions — $100–$500/month — have an outsized impact over 20–30 years due to compound growth. Try adding a monthly amount and see the difference.