Research Guide
How to Calculate NPS
The Net Promoter Score formula, how to classify promoters, passives and detractors, a worked example, and the caveats about small samples and timing.
The Net Promoter Score (NPS) is a single-number measure of customer loyalty based on one question: "How likely are you to recommend us to a friend or colleague?" on a 0–10 scale. It was introduced by Fred Reichheld in a 2003 Harvard Business Review article.
NPS is simple to compute, but small details — how you classify the scale, and how many responses you have — materially affect the number.
The formula
Classify every response: 0–6 are detractors, 7–8 are passives, and 9–10 are promoters. The score is the percentage of promoters minus the percentage of detractors: NPS = %promoters − %detractors. Passives are counted in the denominator but do not contribute to the score.
Because it is a difference of two percentages, the score ranges from −100 (everyone is a detractor) to +100 (everyone is a promoter).
Worked example
Suppose 20 customers answer: 10 give 9–10 (promoters), 5 give 0–6 (detractors) and 5 give 7–8 (passives). That is 50% promoters and 25% detractors, so NPS = 50 − 25 = +25. The PanelRoster NPS calculator does exactly this from your 0–10 ratings.
Interpreting the score
NPS is a benchmark, not a percentage. A score above 0 is positive, above 50 is considered strong in many industries, and benchmarks differ substantially by sector and market. Compare your score over time and against your own industry benchmark rather than treating any single number as a universal pass/fail.
Caveats
NPS is sensitive to small samples — a handful of responses can move it dramatically, so report the response count alongside the score. It also varies with when you survey (post-purchase versus post-support) and with the sample invited. NPS measures stated loyalty intention, not behaviour; it should be one input among several, not a complete customer-health metric.
Key takeaways
- NPS = %promoters (9–10) − %detractors (0–6); passives (7–8) are ignored in the score.
- The score ranges from −100 to +100 and is a benchmark, not a percentage.
- Small samples make NPS unstable — always report the response count.
- Interpret against your industry benchmark and over time, not in isolation.
Tools used in this guide
Related guides
References
- Reichheld (2003) — The One Number You Need to Grow, Harvard Business Review
- Net Promoter System — official NPS definition
References are provided for further reading; PanelRoster is not affiliated with the linked resources.