How do you determine the ROI on your marketing and sales investments? The standard formula is simple: divide the return, less investment, by the investment. A marketing campaign costs $1000, and reaches out to 1000 prospects. Five per cent of these respond, generating $1000 profit, for an ROI of zero: (1000-1000)/1000. If the profit is $1500, then ROI is 50 per cent, if profit is $500, then the ROI is negative.