THE NUMORIX GUIDE
How to use the Mutual Fund Calculator
Last reviewed September 14, 2026
What this calculator does
The projection subtracts a monthly expense-ratio charge from the current balance, applies the net annual return divided by 12, and adds the monthly contribution.
Formula and method
The projection subtracts a monthly expense-ratio charge from the current balance, applies the net annual return divided by 12, and adds the monthly contribution. Net annual return is entered annual return minus expense ratio. Total contributed is initial investment plus monthly contributions, growth is balance minus contributions, and after-tax value applies the entered tax rate to that growth.
Variables and inputs
Enter initial investment, monthly contribution, expected annual return, investment period in years, expense ratio, and tax rate. Money values are dollars; years is the number of monthly cycles divided by 12; return, expense, and tax are percentages.
Worked example
With $10,000 initially, $500 monthly, 7% expected return, and a 0.5% expense ratio, the first month's fee is 10,000 x (0.005 / 12) = $4.17. The remaining $9,995.83 grows at (0.07 - 0.005) / 12 = 0.0054167, then the $500 contribution is added, giving a balance of about $10,549.97 after month 1.
How to interpret the result
The future value is a constant-return scenario after the modeled expense drag. Total fees show the cumulative balance charges, while after-tax value applies a simplified tax percentage to investment growth. Contributions and returns should be compared with the account's actual fee and tax structure.
Common mistakes to avoid
Do not subtract the expense ratio from the return and also enter a second fee elsewhere. Keep annual percentages in percent units. Do not interpret after-tax value as a tax-lot or capital-gains calculation.
Assumptions and limitations
The engine charges a monthly expense ratio and applies a constant net return, but it does not model fund turnover, loads, transaction fees, distributions, tax lots, market losses, or contribution timing within a month. Expense ratios and returns can change.