Definition
Net Promoter Score (NPS) is a loyalty metric built from one question, how likely a customer is to recommend a company, answered on a 0 to 10 scale. The score is the percentage of promoters minus the percentage of detractors, from -100 to 100.
How NPS works
Fred Reichheld of Bain & Company introduced the measure in a 2003 Harvard Business Review article. The survey asks how likely the customer is to recommend the company to a friend or colleague, from 0 to 10. Answers are grouped:
- Promoters answer 9 or 10.
- Passives answer 7 or 8.
- Detractors answer 0 to 6.
NPS = % promoters - % detractors
Passives count in the total of responses but not in the score. The result is a whole number between -100 (everyone is a detractor) and 100 (everyone is a promoter), and it is written without a percent sign.
Two features limit what the number can say. It collapses an 11-point answer into three groups, so a move from 6 to 7 changes the score and a move from 7 to 8 does not. And it is a relationship measure, so it reflects the whole experience with a company over time, not what happened on one call.
Why it matters for voice agents
NPS is a poor way to judge a single voice agent call, and it is worth saying so before a team tries. One automated call is a small part of what a customer thinks of a company, and the score moves slowly. If NPS dips the week an agent launches, the cause could be pricing, a delivery problem or the agent, and the number cannot tell them apart.
It fits better as a trend over months, split by whether the customer’s recent contacts were automated. A “transactional” version of the question, asked right after a call, exists and gets used, but it behaves more like CSAT and should be tracked as a separate series.
For call-level judgement, use outcomes such as resolution rate and first call resolution. NPS then confirms, slowly, whether better calls are changing how customers feel.
Example
An illustrative survey of 200 customers (invented numbers): 90 answer 9 or 10, 70 answer 7 or 8, and 40 answer 0 to 6.
Promoters are 45% and detractors are 20%, so NPS is 45 - 20 = 25.