Last updated: August 6, 2026
Free Compound Interest Calculator
Enter a starting amount, a monthly contribution, an interest rate, and a timeframe to see how much your money could grow. This calculator illustrates the same principle behind dollar-cost averaging and automated retirement contributions — consistent contributions plus time are what compound growth actually rewards.
| Total contributed: | $0 |
| Total interest earned: | $0 |
| Final balance: | $0 |
How to Use This Calculator
- Enter a starting amount, if any — this can be $0 if you're starting from scratch.
- Enter a monthly contribution you plan to add consistently.
- Enter an expected annual interest rate — this is an assumption, not a guarantee, since actual investment returns vary year to year.
- Enter the number of years you plan to let the money grow.
Why Time Matters More Than the Starting Amount
This calculator makes visible what's often described but rarely seen directly: the earlier you start, the more of your final balance comes from growth rather than your own contributions. Try entering the same monthly contribution with 10 years versus 30 years — the difference in total interest earned, not just total contributed, illustrates why starting early is repeatedly emphasized in our retirement planning guide.
A Note on the Interest Rate Assumption
Unlike a savings account with a stated rate, investment returns aren't fixed or guaranteed — a 7% annual rate is a commonly used long-term historical average assumption for diversified stock market investments, but any individual year (or even decade) can vary significantly above or below that average. Use this calculator to understand the mechanics of compound growth, not as a guaranteed projection of actual future returns.
Frequently Asked Questions
What interest rate should I use for a retirement account?
There's no single correct answer, since actual returns depend on your specific investments and market performance over your timeframe. Many long-term retirement projections use a conservative-to-moderate historical average as a planning assumption, but it's worth running the calculator at a few different rates to see a range of possible outcomes rather than relying on a single number.
Does this calculator account for taxes?
No — it shows raw compound growth without factoring in taxes, which vary based on account type (a Roth account, a traditional account, or a taxable account) and your individual tax situation. See our Traditional vs. Roth IRA guide for how account type affects the tax treatment of this growth.
Does this calculator save my data?
No — it runs entirely in your browser, and the numbers you enter aren't sent to or stored on our servers.
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Where to Go Next
Related guides on ClearCents:
Start the Habit This Month
The numbers in this calculator only become real through consistent contributions over years, not a single lump sum or a plan you intend to start "someday." If you're not yet contributing regularly to a retirement or investment account, that's the actual next step.
Ready to open an account? Our guide to investing apps for beginners covers where to actually start.