Compound Interest Calculator
See exactly how compound interest grows your money over time. Add regular contributions to see your full savings potential.
Investment details Compound interest
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S&P 500 avg: ~10% | HYSA: ~4.5%$
Final balance
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Total interest earned
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Total contributions
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Year-by-year growth
| Year | Balance | Interest earned | Total contributed |
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Frequently asked questions
What is compound interest? ›
Compound interest is interest calculated on both your initial principal AND the interest you have already earned. This creates exponential growth over time — often called the "snowball effect." For example, $10,000 at 7% for 30 years grows to about $76,123 with simple interest but $81,165 with annual compounding (and much more with more frequent compounding).
How does compounding frequency affect growth? ›
More frequent compounding produces slightly higher returns. Daily compounding yields marginally more than monthly, which yields more than annual. The difference becomes significant over long periods. For most savings accounts and investments, monthly compounding is standard.
What is the Rule of 72? ›
The Rule of 72 is a quick mental math shortcut to estimate how long it takes to double your money. Simply divide 72 by your annual interest rate. At 6%, your money doubles in approximately 72 ÷ 6 = 12 years. At 9%, it doubles in 8 years. It's a helpful rule of thumb for comparing investment options quickly.
How important are regular contributions? ›
Regular contributions are often more powerful than the initial investment, especially over long periods. Adding $200/month to a $10,000 investment at 7% for 20 years results in a balance of over $122,000 — compared to just $38,700 without contributions. Starting early and contributing consistently is the most impactful factor in wealth building.
About this compound interest calculator
Our compound interest calculator shows you the true power of long-term saving and investing. Enter your principal, interest rate, time horizon, and optional monthly contributions to see your projected balance year by year.
The power of starting early
Time is the most powerful variable in compound interest. A 25-year-old investing $5,000/year at 7% will have approximately $1.1 million at 65. A 35-year-old doing the same has only about $530,000 — roughly half — despite investing for only 10 fewer years. Every year you delay costs disproportionately more than the year before.