NPS calculator
Enter the number of promoters, passives and detractors, or paste the individual scores from your export, and the calculator works out your Net Promoter Score along with its margin of error. Everything is calculated in your own browser: nothing you enter is sent anywhere.
How the calculator works
The Net Promoter Score is the percentage of promoters (9 and 10) minus the percentage of detractors (0 to 6). Passives (7 and 8) count towards the total, but not in the subtraction. That's how Bain & Company defines NPS.
An example. Of 250 customers, 110 are promoters, 85 passives and 55 detractors. That's 44% promoters and 22% detractors, so an NPS of +22.
If you paste individual scores, the calculator sorts them into groups for you. Anything that isn't a whole number from 0 to 10 is skipped, and you'll see how many values that was. Handy for an export that includes empty cells or column headings.
How many responses do you need?
The more responses, the smaller the margin of error. The table shows the approximate margin for an NPS of +20 (40% promoters, 20% detractors) at 95% confidence:
| Responses | Margin | Likely between |
|---|---|---|
| 50 | ±21 | −1 and +41 |
| 100 | ±15 | +5 and +35 |
| 200 | ±10 | +10 and +30 |
| 400 | ±7 | +13 and +27 |
| 1,000 | ±5 | +15 and +25 |
To detect a five-point shift, then, you need hundreds of responses per round. With smaller numbers, only large movements mean much. The calculator uses the standard approximation for the difference between two shares of the same sample:
What the margin of error doesn't cover. The formula assumes the customers who responded are like those who didn't. If it's mostly your fans who reply, or your angriest customers, your NPS will be off in a way no margin can show.
What next?
Compare your NPS above all with your own earlier results, measured the same way and at the same point in the customer journey. To find out what's behind the number, read What is NPS?, which sets out how to get from score to action. Not sure NPS is the right measure for what you want to know? See NPS vs CSAT vs CES.
Sources
- Measuring Your Net Promoter Score, Bain & Company
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