Calculator
Compound Interest Calculator
Compound interest is interest earned on both your original money and interest already credited. This calculator estimates a future balance from a starting amount, ongoing monthly contributions, a nominal annual rate, and compounding frequency.
Investment details
Results
Final balance
$196,665.39
Total contributions
$82,000.00
Total interest earned
$114,665.39
Estimated growth
Yearly illustration of contributions versus estimated balance. This is not a market forecast.
These calculators and articles are for informational purposes only and should not be considered financial, investment, tax, legal, or professional advice.
How this calculation works
Compound interest is interest calculated on both principal and previously earned interest. This tool converts your chosen compounding frequency into an equivalent monthly rate so monthly contributions stay on a consistent timeline.
The result is an illustration at a constant rate. Bank products may quote a compounding APY. Investment accounts do not grow at a fixed rate, so treat market-style inputs as a scenario, not a forecast.
A = P(1 + r/n)^(n t) plus the future value of monthly contributions
P is the starting amount, r is the annual rate, n is compounding periods per year, and t is years. Contributions are modeled monthly using an equivalent monthly rate.
Example
Start with $10,000, add $300 a month, assume 7% a year compounded monthly, and wait 20 years. Contributions total $82,000. The estimated ending balance is higher because interest is credited along the way. Changing the rate or the timeline moves the ending value quickly.
Frequently asked questions
Is the rate a guaranteed return?
No. Bank products may quote a compounding rate. Investment returns vary. This calculator assumes a constant rate so you can see the math, not future performance.
When are contributions added?
The model treats contributions as monthly and converts your compounding frequency into an equivalent monthly rate so the timeline stays consistent.
Why does compounding frequency change the result only slightly?
At the same nominal annual rate, moving from monthly to daily compounding usually adds a small amount. Time, contributions, and the rate itself have a larger effect.
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