Return on Investment (ROI) is one of the most important metrics for evaluating whether an investment, business decision, or project was worthwhile. This ROI calculator computes both the percentage return and the absolute profit or loss based on your initial investment amount and the final value or returns received. It's useful for evaluating stock investments, real estate purchases, marketing campaigns, business projects, or any scenario where you've put money in and want to measure what came out. Comparing ROI percentages across different investment options helps you make more informed decisions about where to allocate your money.