To assess the efficiency of marketing campaigns, marketers use various metrics. Some are focused exclusively on expenses, others on revenue, and others on the return on marketing investment (ROI) — the ratio of revenue to expenses. In this article, we discuss cost per lead (CPL) — one of the most useful and interesting performance indicators — and an advertising model based on it. Let’s take a look at how to calculate the cost of an attracted lead and see which businesses should do so.