In the Net Promoter System, customers are categorised into three groups – promoters (rating 9-10), detractors (rating 0-6), passives (rating 7-8). When calculating the score, the percentage of detractors is subtracted from the percentage of promoters. Passives are excluded.   Example of 10 customer replying to the NPS question: 7 promoters (70%), 1 Detractor (10%), 2 Passives (20%)  70%-20% = NPS 50