Compound interest calculator

How to calculate it

FV = P × (1 + i)^M + C × ((1 + i)^M − 1) / i

P is the initial balance, C is the monthly contribution, and M is the number of months. The monthly rate is i = (1 + r/m)^(m/12) − 1, where r is the nominal annual rate and m is the selected number of compounding periods per year. Beginning-of-month contributions multiply the contribution term by (1 + i). At a zero rate, the balance is P + C × M.

Reference: Investor.gov: compound interest calculator.

Worked example

Starting with 10,000 and adding 100 at each month-end for ten years at 5% nominal annual interest, compounded monthly, produces 31,998.32. Total deposits are 22,000 and interest earned is 9,998.32.

Assumptions and limits

• Contributions are monthly, even when you choose a different compounding frequency. The calculator converts that frequency to an equivalent monthly growth rate; it does not model a bank’s daily deposit or interest-crediting rules.
• The annual rate is nominal. Yearly, quarterly, monthly, and daily compounding mean 1, 4, 12, and 365 periods per year. Use a whole number of months for the time horizon.
• The rate and contribution remain constant and nonnegative. Taxes, fees, inflation, and withdrawals are excluded. An assumed investment return is a scenario, not a guaranteed result.

Results use unrounded inputs and normally display two decimal places. Very small or large numbers may use scientific notation. Use consistent currency units; no currency conversion is applied.

Common questions