Return on Investment

Return on investment (ROI) is a simple measure of how much you gained or lost on something compared with what you put into it, usually shown as a percentage. Spend a sum on a marketing campaign and earn more back, and the return on investment tells you how worthwhile that spend was.

It is like judging a fruit tree by how much fruit it bears against the cost of planting and watering it. Return on investment matters because it lets a business compare very different choices on the same footing, and steer money towards what actually pays off rather than what merely feels busy.