Your financial inputs stay in your browser. The calculator does not require an account and does not upload the amounts you enter for processing.
How to Use the Compound Interest Calculator
- Enter the starting principal.
- Enter the nominal annual interest rate.
- Enter the number of years.
- Choose how often interest compounds; monthly is selected by default.
- Review the projected balance and total interest earned.
How Compound Interest Works
Compound interest adds each period’s interest to the balance before the next period is calculated. The calculator uses A = P(1 + r/n)^(nt), where P is principal, r is the annual rate as a decimal, n is the number of compounding periods per year, and t is time in years.
More frequent compounding produces a slightly higher balance when the principal, nominal rate, and time are otherwise the same. The difference is often small for ordinary rates, but it grows over longer periods.
Compound Interest Example
$10,000 at 5% for 10 years
With monthly compounding, P is 10,000, r is 0.05, n is 12, and t is 10. The projected balance is about $16,470.09, including about $6,470.09 of interest.
Nominal Rate, APY, and Compounding Frequency
A nominal annual rate states the rate before the effect of within-year compounding. Annual percentage yield, or APY, includes that effect. This calculator accepts a nominal annual rate, so a quoted APY should not be entered as though it were the nominal rate.
What This Projection Does Not Include
Real accounts may have changing rates, recurring contributions, withdrawals, taxes, management fees, minimum-balance rules, and rounding policies. Compare the result with the institution’s stated APY and terms before making a financial decision.