How To Calculate NPS (Net Promoter Score)

The equation explained

How To Calculate NPS

NPS (Net Promoter Score) is calculated based on the results of asking a single, simple question. The standard NPS question is:
"How likely is it that you would recommend [product or brand] to a friend or colleague?"

A respondent is asked to answer this question using a scale graduated from:
0 (='Not at all likely') to 10 (='Extremely likely')

NPS question and survey

The NPS methodology splits answers into three groups, based on the score given by a respondent:
Scores of 0-6 are called detractors
Scores of 7-8 are called passives
Scores of 9-10 are called promoters

NPS respondent scale

The NPS score for a period of time (typically, a day or a month) is calculated by subtracting the percentage of detractors from the percentage of promoters. (The passives do not count in the scoring.)

The score is displayed as a number (not as a percentage) within the range of -100 to +100.

NPS equation

Worked example:

In a day, there are 10 respondents and they score:
3, 4, 5, 6, 8, 8, 8, 9, 10, 10
This equates to:
4x detractors (3. 4. 5. 6)
3x passives (8. 8. 8)
3x promoters (9, 10, 10)

So the day's NPS = -10 (calculated by: 30% promoters - 40% detractors = -10)

Rolling or Averaged NPS Scores

Many companies use internal reports and metrics based on rolling or averaged 3 and 12 month NPS scores. This is used to remove the variations that often occur day-to-day or month-to-month (so-called noise). By using a 3-month rolling average, you can often see the trend more clearly that viewing a daily report.

To calculate a 3-month rolling average, the current month's score is calculated by adding up the last three months' scores and dividing by three.

SightMill includes trend analysis to allow you to compare daily, monthly, 3-monthly and 12-monthly graphs of the data to spot trends whilst still being able react quickly to changes.


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