What this calculator measures
Compound growth earns a return on both the original balance and earlier accumulated returns. Regular contributions can eventually contribute more to the ending balance than the initial deposit, so the calculator separates money contributed from modeled growth.
The projection uses one constant rate and does not model volatility, tax, fees or inflation. It is best used for scenario comparison rather than predicting an actual investment balance.
How to use the Compound Interest Calculator
- Enter the starting balance and monthly end-of-period contribution.
- Choose a nominal annual rate, time horizon and compounding frequency.
- Compare ending value, total contributions and modeled compound growth.
The selected nominal annual rate and compounding frequency are converted to an equivalent monthly rate for the month-by-month projection.
Worked example
Starting with $10,000, adding $500 at the end of every month and modeling 6% annual interest for 10 years produces a result that separates $70,000 of contributions from compound growth.
Assumptions and limitations
- A constant rate does not represent real market volatility or sequence risk.
- Taxes, fees and inflation are excluded.
- Contributions are assumed to occur at the end of each month.
- This is an educational projection, not an investment guarantee or recommendation.