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Compound Interest Calculator

See how an initial amount plus regular contributions can grow over time with compound interest. Compare what you put in against the interest you earn.

Estimated future balance
$0
Total contributed
$0
Total interest earned
$0
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How compound interest works

Compound interest earns interest on both your original balance and the interest already added. The starting amount grows by P(1 + r/m)mt, where r is the annual rate, m is the number of compounding periods per year, and t is years. Regular contributions are compounded as an annuity. This calculator deposits contributions each compounding period and applies the period rate to the whole balance.

Frequently asked questions

Does compounding frequency matter?

Yes, but the effect is modest. Daily compounding earns slightly more than annual compounding at the same stated rate, because interest is added more often. The contribution amount and time horizon matter far more.

Are contributions added before or after interest?

This calculator adds each contribution at the start of the compounding period, so the full balance earns the period's interest. Different tools may assume end-of-period deposits, which gives a slightly lower total.

Does this account for inflation or taxes?

No. The result is a nominal balance. Real purchasing power will be lower after inflation, and investment gains may be taxable depending on the account type.

What rate should I use?

Use a realistic long-run return for your investment. Savings accounts pay low rates; diversified stock portfolios have historically returned more but with risk. Past returns do not guarantee future results.

Why is the interest earned so large over time?

Because returns compound: each year's interest joins the principal and earns interest itself. Over decades, this snowball effect can make interest exceed the amount you contributed.

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Disclaimer: This tool provides an estimate for general informational purposes only and is not financial advice. Investment returns are not guaranteed and may be negative. Consult a licensed financial professional before investing.