Compound Interest Calculator
See how savings grow when interest compounds, with optional monthly contributions.
Runs in your browser. Nothing you enter is uploaded.
01How to use the Compound Interest Calculator
- 01Enter your starting deposit and annual interest rate.
- 02Choose how often interest compounds and for how many years.
- 03Add a monthly contribution, or leave it at 0, to see the final balance and interest earned.
02Compound interest formula
A = P × (1 + r/n)^(n·t) + C × ((1 + i)^m − 1) ÷ i P = initial deposit r = annual rate (decimal) n = compounds per year t = years C = monthly contribution, m = months (12·t) i = (1 + r/n)^(n/12) − 1, the equivalent monthly rate
03Examples
$10,000 at 5% compounded monthly for 10 years grows to $16,470.09 with no contributions.
Adding $100 a month to the same account gives about $31,998.
$1,000 at 6% compounded annually doubles in about 12 years.
04Frequently asked questions
What is the difference between APR and APY?
APR is the stated annual rate. APY includes the effect of compounding within the year, so it is slightly higher whenever interest compounds more than once a year.
Does compounding frequency matter much?
Less than people expect. At 5%, moving from annual to daily compounding raises the yield from 5.000% to about 5.127%.
Are taxes included?
No. Interest in a taxable account is usually taxed each year, which lowers the real growth. Tax-advantaged accounts work differently.