The Net Promoter Score (NPS) is the key metric of the Net Promoter System. It is measured by asking "the ultimate question" that allows companies to track promoters and detractors, producing a clear measure of an organization's performance through its customers' eyes. Bain analysis shows that sustained value creators—companies that achieve long-term profitable growth—have NPS two times higher than the average company. And Bain's Net Promoter System leaders on average grow at more than twice the rate of competitors.

To calculate NPS, start with the ultimate question, "How likely are you to recommend us to a friend or colleague?" and score the answers on a zero-to-ten scale. Your Net Promoter Score is simply the percentage of customers who are promoters (those who scored 9 or 10) minus the percentage who are detractors (those who scored 0 to 6).

Measuring your Net Promoter Score gives you a number you can compile and track regularly, not only for a whole company but also for each business, product, store or customer-service team. You can also track it for customer segments, geographic units or functional groups. It helps everyone focus on the twin goals of creating more promoters and fewer detractors. It is, quite simply, your customer balance sheet.

We score the answers to the ultimate question on a simple zero-to-ten scale. This scale is familiar and easy for customers to understand. First, it avoids people mixing up the ends of the scale by erroneously selecting "one" on a one-to-ten scale (a zero is never a good score). Second, it provides enough choice so respondents don’t default to a score of "five out of five" for satisfactory experiences.

With the 11-point scale, we see actual behavioral differences from those who score nines and tens versus those who score zeroes and sixes. These behavioral differences are linked to economic value, the true power of understanding your NPS.