THE NUMORIX GUIDE
How to use the ROI Calculator
Last reviewed September 14, 2026
What this calculator does
The calculator subtracts cost from gain to get net profit, then divides net profit by cost and multiplies by 100: ROI = (gain - cost) / cost x 100.
Formula and method
The calculator subtracts cost from gain to get net profit, then divides net profit by cost and multiplies by 100: ROI = (gain - cost) / cost x 100. The displayed calculation steps repeat the dollar subtraction and percentage division.
Variables and inputs
Enter gain from investment and cost of investment. Both are dollar amounts, and cost must be positive. The route has no holding-period, cash-flow timing, fee, tax, or inflation field.
Worked example
If gain from the investment is $15,000 and cost is $10,000, net profit is 15,000 - 10,000 = $5,000. ROI is 5,000 / 10,000 x 100 = 50%.
How to interpret the result
A positive ROI means the entered gain exceeds the entered cost; a negative ROI means it does not. Basic ROI is a ratio of amounts and is not annualized, so a 50% ROI over one month is not the same investment result as 50% over ten years.
Common mistakes to avoid
Use the original investment cost as the denominator when that is the question being asked. Do not call the gross gain the profit unless cost has already been removed. Keep the holding period separate from the ROI percentage.
Assumptions and limitations
The engine does not validate gain, does not annualize, and does not include transaction fees, taxes, dividends, interim cash flows, inflation, or changing investment value. It cannot compare investments held for different lengths of time fairly without an additional time-based measure.