Compound Interest Calculator
Calculate how a principal amount grows over time with compound interest and optional regular contributions.
How the calculation works
Divides the annual rate by how many times a year it compounds to get a per-period rate, then compounds the starting principal over the total number of periods (years times compounding frequency). Any recurring contribution is treated as happening once per compounding period and grows using the same formula. More frequent compounding produces a slightly larger ending balance for the same nominal annual rate.
Formula
Ending Balance = Principal × (1 + r)^n + Contribution × [((1 + r)^n − 1) ÷ r], where r is the interest rate per compounding period and n is the total number of periods.
Examples
$10,000 principal, 5% annual rate, monthly compounding, 10 years, no contributions
$16,470.09 ending balance ($6,470.09 interest earned)
$5,000 principal, 6% annual rate, annual compounding, 20 years, $1,000/year contribution
$52,821.27 ending balance ($27,821.27 interest earned)