How to do it...

Create a measure using the following formula:

NPS = 
    VAR __TotalResponses = COUNTROWS('R04_Table')
    VAR __Detractors = COUNTROWS(FILTER('R04_Table',[Score] <= 6))
    VAR __Promoters = COUNTROWS(FILTER('R04_Table',[Score] >= 9))
    VAR __PercentDetractors = DIVIDE(__Detractors, __TotalResponses, 0)
    VAR __PercentPromoters = DIVIDE(__Promoters, __TotalResponses, 0)
RETURN
    (__PercentPromoters - __PercentDetractors) * 100