About the Compound Interest Calculator
Estimate how an initial savings balance and monthly contributions grow under a constant nominal interest rate.
Formula or method
Future value = initial balance × (1+r)^n + contribution × ((1+r)^n − 1) ÷ r. With zero rate, add all deposits directly.
Worked example
Starting with 1,000, adding 100 at the end of each month and earning 0% for one year produces 2,200. Positive rates increase the modeled ending balance.
How to use the tool
Start with the example values above, then replace each input with your own figures. The results update immediately. Review the units, denominators, and assumptions before using any number in an important decision.
Assumptions and limitations
This is not an investment forecast. The model assumes a constant rate, monthly compounding and end-of-month contributions; taxes, fees and inflation are excluded.
Frequently asked questions
Is compounding the same as guaranteed growth?
No. Investment returns fluctuate. The calculator is a hypothetical scenario based on the rate you enter.
Privacy and support
Your inputs are processed locally in your browser. ToolMosaic does not upload or store the values you enter in this tool. Our tools are free, and we appreciate your support.