How to calculate NPS: formula, worked examples, and common mistakes
To calculate NPS, group your 0–10 responses into promoters (9–10), passives (7–8), and detractors (0–6), then subtract the percentage of detractors from the percentage of promoters: NPS = %promoters − %detractors. For example, with 250 responses split into 120 promoters, 80 passives, and 50 detractors, NPS = 48% − 20% = 28. The result is always a whole number between −100 and +100.
What is the NPS formula?
NPS = %promoters − %detractors
That is the entire formula. The work is in classifying responses correctly. The NPS question asks 'How likely are you to recommend us to a friend or colleague?' on a 0–10 scale, and every response falls into exactly one of three buckets:
| Score given | Group | Counts in formula as |
|---|---|---|
| 9 or 10 | Promoter | Adds to %promoters |
| 7 or 8 | Passive | Counts in the total only — neither adds nor subtracts |
| 0 through 6 | Detractor | Adds to %detractors |
Note how wide the detractor band is: a seemingly decent 6 out of 10 is a detractor. This is by design — the methodology treats anything below 7 as a churn and negative-word-of-mouth risk.
How do you calculate NPS step by step?
- 1Count total responses to the 0–10 question (exclude skips and blanks)
- 2Count promoters: responses of 9 or 10
- 3Count detractors: responses of 0 through 6
- 4Calculate %promoters = promoters ÷ total × 100
- 5Calculate %detractors = detractors ÷ total × 100
- 6Subtract: NPS = %promoters − %detractors, rounded to a whole number
Worked example 1: a typical mid-size sample
You collect 250 responses: 120 people answered 9 or 10, 80 answered 7 or 8, and 50 answered 0–6.
- %promoters = 120 ÷ 250 × 100 = 48%
- %detractors = 50 ÷ 250 × 100 = 20%
- NPS = 48 − 20 = 28
The 80 passives never enter the subtraction, but they matter: they are 32% of your total, diluting both percentages. If 20 of those passives became promoters next quarter, NPS would jump to 56 − 20 = 36.
Worked example 2: a negative score
You collect 80 responses: 18 promoters, 22 passives, 40 detractors.
- %promoters = 18 ÷ 80 × 100 = 22.5%
- %detractors = 40 ÷ 80 × 100 = 50%
- NPS = 22.5 − 50 = −27.5, reported as −28 (or −27 if you round half toward zero — pick one convention and keep it)
A negative NPS simply means detractors outnumber promoters. Half of this sample is at risk — the score is telling you to go read the detractor comments before doing anything else.
Calculate NPS in a spreadsheet with three COUNTIF formulas (one per bucket) rather than by hand. It eliminates classification errors and gives you a reusable template: =COUNTIF(range,">=9") for promoters, =COUNTIF(range,"<=6") for detractors, then the subtraction.
What mistakes skew an NPS calculation?
- Counting 7s and 8s as promoters — passives are excluded from the top of the formula, full stop
- Reporting NPS as a percentage — it is a score (NPS of 28, not 28%)
- Averaging the 0–10 responses instead of using the bucket formula — an average of 7.8 is not an NPS
- Including blank or skipped responses in the total, which silently deflates both percentages
- Mixing survey channels mid-stream — in-app responses and email responses often score differently, so a channel switch can move the score without anything real changing
- Reading too much into tiny samples — with 20 responses, one person switching buckets moves the score by 5 points
How many responses do you need for a reliable NPS?
More than most teams expect. Because NPS is a difference of two percentages, its margin of error is wider than a single percentage's. With 100 responses, swings of several points between waves are usually noise. As a practical rule, treat scores from fewer than 100 responses as directional, and avoid celebrating or panicking over moves smaller than your sample can support. If your customer base is small, survey everyone and focus on the verbatim comments instead of the score.
To collect the data itself, any tool with a 0–10 question works. Formkii's free survey maker includes a dedicated NPS question type and CSV export, so you can run the survey and drop the results straight into your spreadsheet formula.
Frequently asked questions
Is a 7 out of 10 a promoter in NPS?
No. Scores of 7 and 8 are passives — they count in your total responses but are excluded from both sides of the formula. Only 9s and 10s are promoters, and 0 through 6 are detractors.
Can NPS be calculated as an average?
No. NPS is not the average of the 0–10 scores. It is the percentage of promoters minus the percentage of detractors, producing a score between −100 and +100. An average hides the distribution that NPS is designed to expose.
Why is NPS not shown as a percentage?
Because it is the difference between two percentages, not a proportion of a whole. An NPS of 28 means the promoter share exceeds the detractor share by 28 percentage points, so it is written as a plain score: 28, not 28%.
What happens to passives in the NPS calculation?
Passives (7s and 8s) are counted in the total number of responses but excluded from the subtraction. They still affect the score indirectly: a large passive group shrinks both the promoter and detractor percentages, pulling the score toward zero.