# NPS calculation formula

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Viewing 13 posts - 1 through 13 (of 13 total)
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• #50682

Hersey
Participant

I know NPS is calculated as % promoters minus % detractors. My question is: are the percentages based on total # of all respondents or total # promoters plus total # detractors (i.e., # of  “passive” responders are omitted from denominator)?

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#174722

I’Anson
Participant

Hi Don,
The %’s are based on total # of all respondents.
Cheers,
Daniel.

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#174925

McNabb
Participant

Our operational definition has NPS caluclated based on the total number of respondents.

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#179544

Moore
Member

How do you calculate the minimum number of scores required to have a statistically accurate result? For example, if I have 250 sales people in the field, how do i know how many NPS scores I need for each in order to accurately compare the results (ie maybe have bonus structure that includes NPS).Any help is most appreciated.Thanks.

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#179623

Marty Yuzwa
Participant

Stuart,
This is the Excel formula that I use to calculate the +/- error percentage for my NPS calculations.
IF(“NPS %”<0.5,(NORMSINV(1-(1-0.95)/2)*SQRT("NPS %"*(1-"NPS %")/"No. of Surveys")),(NORMSINV(1-(1-0.95)/2)*SQRT("NPS %"*(1-"NPS %")/"No. of Surveys")))
The sample size will then depend on the how tight you need the error to be.
To give you an idea, if the NPS Score was at 50%, then a sample of 100 surveys would give +/- 10%.  A sample of 200 surveys would be +/- 7%.  It would take about 2000 surveys to get to +/- 2%.I  find that in order to get all the samples I need I have to use a rolling 6 month or rolling 12 month NPS Score.

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#189262

Brian Carson
Participant

“if the NPS Score was at 50%, then a sample of 100 surveys would give +/- 10%.”  Does this mean that the actual NPS is between 40%-60%? or between 45% – 55%?

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#189267

Ken Feldman
Participant

What do you think? Is 50% plus 10% equal to 55%?

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#189295

Brian Carson
Participant

My question is to clarify if the 10% is 10 points of NPS (50 + 10 = 60) or is it 10% of the current NPS score (50 x 10% = 5…..50 + 5 = 55)?

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#189296

Brian Carson
Participant

My question is to clarify if the 10% is 10 points of NPS (50 + 10 = 60) or is it 10% of the current NPS score (50 x 10% = 5…..50 + 5 = 55)?

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#189298

Ken Feldman
Participant

This is what you posted:
if the NPS Score was at 50%, then a sample of 100 surveys would give +/- 10%All units are in % so why would you think otherwise?

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#189300

Brian Carson
Participant

“if the NPS Score was at 50%, then a sample of 100 surveys would give +/- 10%.”  comes from the post by Marty Yuzwa.  I am asking for clarification.

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#189304

Ken Feldman
Participant

Hopefully it is clarified or you can wait around for Marty to respond.

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#189337

Marty
Participant

:)

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