THE NUMORIX GUIDE
How to use the Investment calculator
Last reviewed September 12, 2026
What this investment calculator does
This calculator models how a starting balance and recurring contributions could grow under an assumed return, contribution frequency, and time horizon. It separates money you contribute from the value attributed to growth so the result is easier to audit.
Compound-growth method
For the live beginning-of-period contribution mode, future value is FV = P(1 + r/m)^(mt) + C[((1 + r/m)^(mt) - 1) / (r/m)](1 + r/m). P is starting principal, C is the contribution per period, r is the annual return, m is the number of compounding periods per year, and t is years. The implementation may rearrange this relationship when solving for another input.
Worked example
With $5,000 invested initially, $300 contributed at the beginning of each month, a 7% annual return, monthly compounding, and a 10-year horizon, the engine uses r = 0.07 / 12 and n = 120. FV = $5,000(1 + 0.07 / 12)^120 + $300[((1 + 0.07 / 12)^120 - 1) / (0.07 / 12)](1 + 0.07 / 12) = $62,276.65 before taxes and fees. Total contributions are $41,000, so the modeled growth is $21,276.65.
How to interpret the result
The output is a scenario, not a promise. Changing the return, contribution timing, fee, or inflation assumption can materially change the outcome. Compare several conservative, middle, and optimistic scenarios instead of treating one projection as a forecast. Contributions made earlier generally have more time to compound, so timing should match the account or plan you are modeling. Use contributions and returns that share the same time units, such as monthly contributions with a monthly compounding convention.
Common mistakes to avoid
Do not compare a nominal return in one scenario with an inflation-adjusted return in another. Match contribution frequency to the account behavior. Include fees and taxes when comparing products, because they reduce the amount that remains invested.
Assumptions and limitations
The model uses a constant assumed return and does not simulate volatility, losses, withdrawals, taxes, fees, inflation, or the sequence in which returns occur unless those inputs are explicitly provided. Actual investments can lose value.