How this calculator works
At each compounding interval, the existing balance earns the equivalent periodic return. Contributions are then added whenever a contribution date coincides with that timeline.
Formula and methodology
Periodic rate = (1 + annual return)^(1 ÷ periods per year) − 1
Values are calculated with full JavaScript numeric precision and rounded only for display.
Example calculation
Model $10,000 initially and $500 monthly for 20 years, comparing monthly, quarterly, or annual compounding.
Understanding your results
Use the output to compare scenarios under consistent assumptions. It is most useful as a planning range: change the return, contribution, or duration and observe how sensitive the estimate is.
Key assumptions and limitations
- Rates and contributions remain constant.
- Contributions occur at period-end.
- Taxes, inflation, and fees are excluded.
Compound Investment Calculator FAQs
What does this compound investment calculator show?
It turns the assumptions you enter into a hypothetical estimate so you can explore long-term scenarios.
Does this calculator predict investment returns?
No. The return is a constant user-provided assumption; real returns vary and may be negative.
Are taxes and inflation included?
No. Results are nominal estimates and exclude taxes and inflation unless a calculator explicitly says otherwise.
When are contributions added?
Recurring contributions are modeled at the end of each selected contribution period.
Are fees included?
Fees are excluded except in the ETF fee calculator, which models expense ratios using a simplified net-return approach.
Can I enter a negative return?
Yes, returns greater than -100% are supported to help test downside scenarios.