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.
Learn how to calculate it yourselfEnter your values
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NPS confidence interval
NPS 50 ± 9.3 points
- NPS
- 50
- Margin of error
- ±9.3
Calculate it yourself
Use 120 promoters, 50 passives and 30 detractors to find NPS and its approximate 95% interval.
Follow this worked example, then repeat the steps with your own numbers.
Find the promoter and detractor proportions
n = 200. pP = 120/200 = 0.60; pD = 30/200 = 0.15. Difference = 0.45.Calculate NPS and its standard error
NPS = 100 × 0.45 = 45. SE = √[(0.60 + 0.15 − 0.45²)/200] ≈ 0.05232.Convert the margin into NPS points
95% margin = 1.96 × SE × 100 ≈ 10.25 NPS points.Add and subtract the margin
Interval = 45 ± 10.25, or approximately 34.75 to 55.25 NPS points.Keep the standard error unrounded when calculating the margin and endpoints.
This is a normal approximation to a multinomial sample. It can be unreliable with small samples or extreme category proportions; it does not clamp interval endpoints to −100 and 100.
Check your answer in the calculatorUse your PaperSurvey.io results
Use the exact promoter, passive and detractor counts from your responses to calculate an NPS interval here.
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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