Return on Investment (ROI) is the actual profit you have made as an affiliate after investing your money for promoting the advertisers products. You have to subtract the total costs from the net revenue to calculate ROI. This simple method is useful in determining the ROI when only direct costs are involved with your marketing campaigns. Sometimes, you have to make advanced ROI calculations when you run an extensive affiliate campaign that includes website development, hosting cost, computers, software, direct campaign costs and office space required to run large campaigns. The ROI is significant because it helps you to determine whether your efforts are worth it.