Net Promoter Score
Also called NPS
The share of people scoring 9 or 10 on a recommend question minus the share scoring 0 to 6, in percentage points.
Ask how likely someone is to recommend the product or service on a 0-to-10 scale. Group responses into promoters (9 or 10), passives (7 or 8), and detractors (0 to 6). Subtract the detractor percentage from the promoter percentage. NPS ranges from −100 to +100, without a percent sign. Passives remain in the denominator.
Discarding the middle is what makes the score move so freely: a few people shifting from 8 to 9 can swing a small sample by several points while opinion has not changed. Below a few hundred answers, most quarter-on-quarter movement is sampling noise, so quote the interval and keep the three shares beside the score.
Use consistent wording, audiences and timing to track NPS. A follow-up question can help explain why someone chose their score.
Where it goes wrong
Benchmarks. Scores are not comparable across industries, audiences or collection methods, and a number described as good by a vendor's benchmark deck means very little about yours.