Return on investment (ROI) is a metric used to evaluate the profitability of an investment. It’s calculated as a ratio between net income (or profit) and the costs of investment. It’s not synonymous with the interest rate. In P2P lending, your ROI will typically account for the received interest payments and other gains (such as bonuses, late fees, secondary market sale premiums, etc.) and losses (e.g., bad debt and platform fees). In short, ROI is a measure of what you get back compared to what you put in.