CSAT and NPS calculator with margin of error
A score from 40 survey answers can move ten points by chance alone. Enter your counts to see the score and how far it could be from the truth, at 95% confidence.
CSAT
83.3%
95% range
72% to 91%
50 of 60 answers were a 4 or 5. With this many answers your underlying CSAT is probably between 72.0% and 90.7%. The average rating is 4.23 out of 5.
CSAT = answers rated 4 or 5 ÷ all answers × 100. The range is a Wilson score interval, which stays honest with small samples.
NPS
+33
Margin of error
± 15.4
50% promoters minus 17% detractors from 90 answers gives 33. A change smaller than about 15 points between two surveys this size could be chance.
NPS = % promoters − % detractors, from −100 to +100. The margin treats each answer as +1, 0 or −1 and takes 1.96 standard errors.
How many answers do you need?
For a share such as CSAT, these are the answers needed for a given margin of error at 95% confidence, in the worst case of a 50/50 split. Scores near 90% need fewer.
| Margin of error | Answers needed |
|---|---|
| ± 10 points | 97 |
| ± 5 points | 385 |
| ± 3 points | 1,068 |
| ± 2 points | 2,401 |
Margins only cover chance. They can’t fix who chooses to answer: if mostly delighted or furious customers reply, the score leans their way however many answers you collect.
Questions
How do you calculate CSAT?
Count the survey answers rated 4 or 5 on a 1 to 5 scale, divide by all answers, and multiply by 100. 50 satisfied answers out of 60 is a CSAT of 83.3%.
How do you calculate NPS?
Ask how likely someone is to recommend you on a 0 to 10 scale. 9s and 10s are promoters, 7s and 8s passives, 0 to 6 detractors. NPS is the percentage of promoters minus the percentage of detractors, so 45% promoters and 15% detractors is an NPS of 30.
Why does my score jump around from week to week?
Mostly chance, when the number of answers is small. With 50 answers, a CSAT can move several points either way with no real change in service. The margin of error above shows how big a move has to be before it means something.
What's the difference between CSAT and NPS?
CSAT asks about one interaction, usually right after a ticket is solved, so it reflects the support experience. NPS asks about the relationship with the company as a whole, so price, product and support all feed into it. Support teams usually own CSAT; NPS is shared.
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