Share of promoters (9-10) minus share of detractors (0-6) on a 0-10 'would you recommend' question; ranges from -100 to 100.
Example
Common mistakes
Writing NPS as a percentage. "NPS 20%" suggests a share of people; the score is a difference of two shares.
Counting 7 and 8 as positive. Passives only count in the total.
Reading every change as real. With a few hundred answers, moves of 5–10 points are often noise; look at the range.
Comparing surveys run differently. A score asked right after a support ticket and one asked in a yearly email are not comparable.
Averaging the 0–10 answers instead. The mean hides how split the answers are.
NPS turns one survey question, "How likely are you to recommend us to a friend or colleague?" on a 0–10 scale, into a single score. Answers of 9 and 10 are promoters, 7 and 8 are passives, 0 to 6 are detractors:
NPS=100×(npromoters−ndetractors)
The result runs from −100 (everyone a detractor) to +100 (everyone a promoter) and is written as a plain number, "NPS 20", not a percentage. Passives count in n, so adding passives pulls the score towards zero without being positive or negative themselves.
NPS from a survey is an estimate. Another sample of the same size would give a different score, and the spread is wider than most people expect because the score is the difference of two shares from the same respondents. Score every answer +1, 0 or −1: the NPS is 100 × their average, and its standard error is 100V/n with V=pP+pD−(pP−pD)2. With 200 answers the 95% range is roughly ±11 points; a ±5 point range takes about 1,000 to 1,500 answers.
The simple ± 1.96 × standard error range breaks down at small samples and lopsided answers (with every answer a promoter it has zero width), so a reliable calculator adds a few imaginary answers first, three quarters of an answer to promoters and to detractors, before building the range.
The same score can hide very different mixes: 40% promoters and 20% detractors, or 20% and 0%, both give NPS 20. Report the three shares next to the score.
CatChow asked customers the recommendation question after their third order. 200 answered: 90 promoters, 60 passives and 50 detractors.
