NPS (Net Promoter Score) is a key metric for measuring customer loyalty, developed by Bain & Company's Fred Reichheld in 2003. It's calculated from a single question: "How likely are you to recommend our product/service to a friend? (0-10)". NPS = %Promoters - %Detractors, ranging from -100 to +100.
NPS > 70 is excellent, 50-70 is great, 30-50 is good, 0-30 is average, and < 0 needs improvement. Industry averages vary — tech companies often score higher (30-40) while telecom/insurance score lower (10-20).
Scores of 9-10: Promoters (loyal customers). 7-8: Passives (satisfied but unenthusiastic). 0-6: Detractors (unhappy customers who may spread negative word-of-mouth).