Calculation of the Net Promoter Score
The Net Promoter Score is calculated as the the difference between your promoter percentage and detractor percentage. The result is a value between -100 (worst value) and 100 (best value).
Customers who selected a 9 or 10 are your promoters. These customers are fans of your product or brand. They willingly give constructive criticism and take time for longer surveys. Promoters often make recommendations to third parties. This behaviour can be promoted through incentives (refer a friend or something similar).
Customers who scored a 7 or 8 are passives. These customers are satisfied. They got what they expected. However, they are no fans of your product or brand. If they find a cheaper product offered by your competitors, they are likely to buy it.
Customers who scored a 6 or less are detractors. These customers are dissatisfied or even disappointed. They spread bad word-of-mouth. This means that they share their bad experiences with third parties and possibly dissuade them from making a purchase from your company.