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Compound Interest Calculator

See how a starting balance plus regular monthly contributions can grow over time. Adjust the rate and time horizon to understand the power of compounding.

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Total you contribute
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Total interest / growth
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Assumes monthly compounding and a constant return. Real returns vary year to year.

Why compounding is so powerful

With compound growth, your returns start earning returns of their own. The two biggest levers are time and consistency — small, regular contributions left to compound for decades often outgrow larger sums invested later.

The formula

For a starting amount that compounds monthly: FV = P(1 + i)N, plus the future value of monthly contributions PMT · ((1 + i)N − 1) / i, where i is the monthly rate and N is the number of months.

Planning specifically for retirement? The Retirement Savings Calculator applies the same math to your retirement timeline. Remember: investing involves risk, including the possible loss of principal.

Frequently asked questions

What is compound interest?
It's interest earned on both your original money and the interest it has already earned. Over time this compounding accelerates growth — which is why starting early matters so much. The same effect works against you on debt.
What rate of return should I use?
Use a realistic, conservative estimate for your situation — a high-yield savings account earns far less than a diversified long-term stock portfolio, and all investments carry risk. This is an illustration, not a prediction; real returns vary year to year and are not guaranteed.
Does this account for inflation and taxes?
No. The result is a nominal projection before inflation, taxes, and fees, which all reduce real-world growth. Treat it as a directional estimate, not a promise.

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