See how savings grow with compound interest. Enter a starting principal, annual rate, investment period, and optional monthly contributions — future balance and interest earned update live.
Interest compounds monthly. Results are estimates — not financial advice.
Frequently Asked Questions
How does compound interest work?
You earn interest on your balance plus previously earned interest. With monthly compounding, the annual rate is applied twelve times per year on the growing balance.
How are monthly contributions handled?
Each contribution is added at the end of every month and compounds with the rest of the balance for all remaining months in the period.
What if the interest rate is 0%?
The future balance equals your principal plus the sum of all monthly contributions with no interest growth.
Can I calculate loans or ROI?
Yes. Try the Loan Calculator for payments or the ROI Calculator for return on investment.
Are taxes or fees included?
No. The calculator shows gross growth before taxes, account fees, or inflation.
Is this tool free and does it work on mobile?
Yes on both counts. The Compound Interest Calculator on draft21 is completely free with no sign-up required and works on all devices.