How to use this tool
Enter your opening balance, monthly contribution and nominal annual interest rate.
Choose how often interest compounds and whether contributions arrive at the start or end of each month.
Monthly growth factor = (1 + nominal rate / periods per year)^(periods per year / 12)
Worked example
$17,175.24 · projected final balance
Fixed example using the settings below. Monetary examples use USD; dates and times use their stated reference values. This example stays unchanged when you edit your calculation.
Example inputs
- Starting principal: 1000
- Monthly contribution: 100
- Nominal annual rate (%): 5
- Time (whole years): 10
- Compounding frequency: Monthly
- Monthly contribution timing: End of month
Method illustration: 1,000 initially plus 100 each month for 10 years at 5% nominal interest compounded monthly reaches about 17,175.24 with end-of-month contributions.
Assumptions and limits
- The effective monthly factor applies consistently between monthly contributions. It is a model, not a bank's actual daily posting schedule.
- Contributions are fixed. Rates stay constant; fees, tax, inflation and investment uncertainty are excluded.
- Only nonnegative rates and contributions are supported. Yearly figures show end-of-year balances.
Method reference: Investor.gov compound interest inputs
Check or report a result
Check the units, selected calculation and assumptions first. Compare the fixed example above with your inputs to identify what changed.
Report a calculation issue with the page address, hypothetical inputs, result displayed and result expected. Do not include passwords, bank details or other private information.