NPS Confidence Interval Calculator
Find the margin of error on your Net Promoter Score. Enter the number of promoters, passives and detractors and pick a confidence level.
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Why NPS has a wide interval
Net Promoter Score is the difference between two proportions, the percentage of promoters minus the percentage of detractors. Because it combines the sampling error of both groups, its confidence interval is wider than the interval on any single percentage. A score of plus 60 from 200 responses can still carry a margin of error of several points.
How it is calculated
The calculator treats promoters, passives and detractors as a multinomial split, then propagates their variances into the NPS difference. It reports the score, the margin of error and the resulting interval at your chosen confidence level. Collecting more responses narrows the interval.
Frequently asked questions
How many responses do I need for a stable NPS?
It depends on how tight an interval you need, but many teams aim for a margin of error of about 5 points or less, which usually means several hundred responses.
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