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Compound Interest Calculator Guide
See how your money grows when interest earns interest. Enter a starting amount, rate, compounding frequency, and optional regular contributions to project the future value.
A = P(1 + r/n)^(nt), where P is the principal, r the annual rate, n the times compounded per year, and t the years. Contributions add a second term for the growth of each deposit.
How Does Compound Interest Work?
Each period, interest is added to your balance, and the next period earns interest on that larger balance. Over time this snowballs. For example, $10,000 at 5% compounded monthly for 10 years grows to about $16,470 with no extra deposits.
Why Compounding Frequency Matters
The more often interest compounds, the faster it grows, though the difference between monthly and daily is small. What matters most is the rate, the time, and how much you add along the way.
| Compounding | Times per year |
|---|---|
| Annually | 1 |
| Quarterly | 4 |
| Monthly | 12 |
| Daily | 365 |
These results are estimates for education and planning, not financial advice. Actual returns, rates, and terms vary — check with a qualified professional before making decisions.
Related: Simple Interest, Savings Goal, and Retirement Calculator.
Frequently Asked Questions
What is compound interest?
It's interest calculated on both your original amount and the interest already added, so your balance grows faster over time.
What is the compound interest formula?
A = P(1 + r/n)^(nt), where P is principal, r the annual rate, n compounds per year, and t the number of years.
How often should interest compound?
More frequent compounding grows a little faster, but the rate and time invested matter far more than the frequency.
Does this include regular contributions?
Yes — add a recurring contribution and the calculator grows each deposit along with your starting balance.
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