Return on investment (ROI) is a way to measure an investment’s performance. It also can be used to compare different investments.

There are multiple ways to calculate returns, and we’ll cover some of them in the next chapter. For now, though, it’s enough to understand that ROI measures the gains or losses compared to the initial investment. In other words, it’s an approximation of an investment’s profitability. Compared to the original investment, a positive ROI means profits, and a negative ROI means losses.

ROI calculation applies to not just trading or investment, but any kind of business or purchase. If you plan to open or buy a restaurant, you should do some number crunching first. Would opening it make sense from a financial perspective? Calculating an estimated ROI based on all your projected expenses and returns may help you make a better business decision. If it seems like the business would turn a profit in the end (i.e., have a positive ROI), it may be worth getting it started.

Also, ROI can help evaluate the results of transactions that already happened. For example, let’s say you buy an old exotic car for $200,000. You then use it for two years and spend $50,000 on it. Now suppose that the car’s price goes up on the market and you can now sell it for $300,000. Not only did you enjoy this car for two years, but it also brought you a sizable return on your investment. How much would that be exactly? Let’s find out.