Compound Interest Calculator

About this tool

This compound interest calculator shows how an initial investment plus optional monthly contributions grows over up to 50 years, with annual, quarterly, monthly or daily compounding. It reports the final balance, total contributed, interest earned and total return.

How to use it

1. Enter your initial investment and the annual interest rate.
2. Add a monthly contribution if you plan to keep investing.
3. Set the time in years and choose how often interest compounds.
4. Read the final balance, total contributed, interest earned and total return.

Good to know

• The initial amount grows as A = P × (1 + r/n)^(n·t), where r is the annual rate, n the compounding periods per year and t the years.
• Example: 10,000 at 7% compounded monthly for 10 years grows to about 20,096.61; compounded annually it reaches about 19,671.51.
• Each monthly contribution is compounded for the time remaining until the end of the period, so earlier deposits earn more interest.
• Total return is interest earned divided by the total amount you contributed.
• The Rule of 72 gives a quick estimate: at 7% a year, money doubles in roughly 72 ÷ 7 ≈ 10.3 years.

Runs entirely in your browser — nothing you enter is uploaded or stored.

Frequently asked questions