Compound Interest Calculator
See how a starting balance and regular monthly deposits grow with compound interest. Change the rate, years and compounding to compare scenarios.
How the compound interest calculator works
Compound interest means you earn interest on your original money and on the interest already added. Each period the balance grows a little faster than the one before, which is why time matters so much for savings and investments.
Enter your starting balance, how much you add each month, the yearly interest rate and the number of years. Pick how often interest compounds. The calculator assumes each deposit is made at the end of the compounding period and that the rate stays the same for the whole time.
The U.S. SEC also offers a compound interest calculator on Investor.gov if you want to compare results.
The formulas
Example: You start with $10,000, add $200 a month and earn 7% a year, compounded monthly, for 10 years. The starting balance grows to $20,096.61 and the deposits grow to $34,616.96, for a total of $54,713.58. You put in $34,000 yourself, so $20,713.58 of the final balance is interest. The 7% rate is an example for illustration, not a prediction or a guaranteed return.
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Frequently asked questions
What is the compound interest formula?
The formula is A = P(1 + r/n)^(nt). A is the final amount, P the starting balance, r the annual rate as a decimal, n the number of times interest compounds each year and t the number of years. Regular deposits add a second part to the formula, shown above.
How often should interest compound?
The more often interest compounds, the more you earn, but the difference between monthly and daily compounding is small. The interest rate and the time you leave the money invested matter far more.
What is the difference between simple and compound interest?
Simple interest is paid only on the original amount. Compound interest is paid on the original amount plus the interest already earned, so growth speeds up over time.
Are the results guaranteed?
No. Savings account rates change and investments go up and down. This calculator assumes one fixed rate for the whole period, so treat the result as an illustration.
Does the calculator include taxes or inflation?
No. Taxes, fees and inflation reduce what you keep and what the money can buy. Try a lower rate to see a more cautious scenario.
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