Free tool
NPS calculator with margin of error
The short answer
Net Promoter Score is the percentage of promoters (who answer 9 or 10) minus the percentage of detractors (0 to 6), giving a score from -100 to 100. With 220 responses, of which 120 are promoters and 40 detractors, NPS is 36, plus or minus about 10 points at 95% confidence.
On this page 6 sections
Net Promoter Score
NPS
36
Margin of error (95%)
±10.2
Responses
220
With 220 responses the score could plausibly be anywhere from 26 to 47. Treat small month-to-month changes as noise.
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How NPS is calculated
Ask "How likely are you to recommend us to a friend or colleague?" on a 0 to 10 scale. Promoters answer 9 or 10, passives 7 or 8, detractors 0 to 6. NPS = % promoters minus % detractors. Passives count toward the total but not the score.
Why the margin of error matters
NPS swings more than a simple percentage because it is the difference of two proportions. The margin of error here uses the standard variance for that difference: (share of promoters + share of detractors - NPS squared) / responses, times 1.96 for 95% confidence. With under 100 responses the margin is often more than 15 points, so a monthly move from 30 to 38 may be nothing.
Getting a useful score
- Ask at a consistent moment (after onboarding, after support, quarterly) so scores are comparable over time.
- Always add an open follow-up question: the reason matters more than the number.
- Compare against your own history, not published industry averages, which use different samples and moments.
- Close the loop with detractors quickly; it is the cheapest retention work there is.
More on running NPS well: how to measure NPS and NPS vs CSAT vs CES. Need enough responses first? Use the survey sample size calculator.
Questions
- What is a good NPS?
- Any score above 0 means more promoters than detractors. Benchmarks vary widely by industry and by when the question is asked, so the most useful comparison is your own score over time, with its margin of error.
- How many responses do I need for NPS?
- For a margin of error around 10 points you typically need 200 or more responses, depending on how answers are split. Enter your counts above to see the margin for your own data.
Sources
Related guides
How to measure NPS (Net Promoter Score)
How to ask the NPS question, calculate the score, choose when and where to survey, and turn the follow-up comments into decisions.
NPS vs CSAT vs CES: which customer metric to use
NPS, CSAT and CES compared: the question each asks, how to calculate it, and when each one is the right measure of customer experience.