DIY Cost Tools
Compound Interest Calculator
FINANCIAL CALCULATOR
Project account growth from an initial balance, monthly deposits, a fixed rate, and monthly compounding.
How it works
The calculator applies one month of interest, then adds the monthly contribution, repeating for the selected number of years.
Formula
New balance each month = previous balance × (1 + annual rate ÷ 12) + monthly contribution.
Worked example
Starting with $10,000, adding $200 monthly, and earning 7% annually for 10 years produces about $54,713.58 under the stated assumptions.
Important limits
- Returns and savings rates can change and may be negative.
- Taxes, fees, inflation, and contribution timing outside month-end are not included.
- The result is a projection, not a guarantee or investment recommendation.
Frequently asked questions
Why does compounding matter?
Interest can earn additional interest in later periods, so time and rate both affect growth.
When are contributions added?
This calculator assumes the monthly contribution is added at the end of each month.
Sources and review notes
The compounding method follows the standard future-value relationship described in investor education materials from the U.S. Securities and Exchange Commission. Last reviewed September 29, 2026.