Compound Interest Calculator
What a sum grows to when interest earns interest, with optional monthly additions.
Result…
How it's calculated
A = P × (1 + r ÷ n)^(n × t) (continuously: A = P × e^(r × t)) Monthly additions C: + C × ((1 + i)^m − 1) ÷ i, i = the equivalent monthly rate
Compound interest adds each period's interest to the balance, so later interest is earned on earlier interest. More frequent compounding raises the effective yearly rate a little. The rate is assumed constant; real savings and investment returns vary.
Your numbers, step by step
About the Compound Interest calculator
Compound interest is interest earned on interest: each period's interest is added to the balance, and the next period's interest is worked out on that bigger balance. This calculator shows what a starting amount grows to at a fixed yearly rate. It handles compounding from yearly to daily or continuously, with an optional amount added every month. It also shows the total you put in, the interest earned and the effective yearly rate. The rate is assumed to stay the same, so treat the result as an illustration: real savings and investment returns rise and fall. To plan toward a target instead, try the savings goal calculator.
How to use it
- Enter the “Starting amount” and the yearly “Interest rate”.
- Enter the “Time” in years.
- Choose how often interest is added under “Compounding”: annually, monthly, daily or continuously, among others.
- Add a “Monthly addition” if you plan to pay in regularly, or leave it at 0.
- Read the future value, then the total put in, the total interest and the effective yearly rate.
Worked example
$10,000 at 5% a year, compounded monthly for 10 years, grows to $16,470.09. Add $100 every month and it reaches $31,998.32: you put in $22,000, and $9,998.32 is interest. Monthly compounding makes the 5% rate worth an effective 5.12% a year.
Updated
Questions people ask
What is the compound interest formula?
A = P × (1 + r ÷ n)^(n × t), where P is the starting amount, r the yearly rate as a decimal, n the number of compounding periods a year and t the number of years. Continuous compounding uses A = P × e^(r × t).
Does compounding more often make a big difference?
A small one. $1,000 at 5% for 10 years becomes $1,628.89 compounded yearly, $1,647.01 monthly and $1,648.72 continuously.
What is the effective yearly rate?
It is the rate that, compounded once a year, gives the same result as the quoted rate compounded more often. 5% compounded monthly works out to about 5.12% a year.
How is compound interest different from simple interest?
Simple interest is paid only on the original amount, so it grows in a straight line. Compound interest is also paid on past interest, so growth speeds up over time. Compare them with the simple interest calculator.
Can I rely on this for investments?
Only as an illustration. It assumes one fixed rate for the whole period, while real returns vary and can be negative. For decisions about your own money, talk to a qualified financial adviser.