The Net Promoter Score, or NPS in short, is a way to measure your customer happiness.
The idea is to only ask one very simple question to measure how likely one person is to recommend a particular brand to a friend. The possible answers range from zero, the lowest score, all the way up to ten, which is the highest score.
Based on her answer, the user is than categorized in three different categories: the promoters, the neutrals and the detractors.
Everyone who answer between 10 and 9 is a Promoter. These are those people who are enthusiastic about your product or service and will actively recommend it to your friends.
Whoever answer between 8 and 7 is defined as Netrual, which means that he is indifferent about your service and won't actively recommend or talk about the product.
Anyone who gave a score of 6 or less is considered a detractor. A detractor is not happy with your product and will actively recommend against using it to his friends and colleagues.
After determing how many promoters, detractors and netruals user your product/service has, it is then possible to calculate the NPS.
The NPS is calculated as the percentage of your Promoters minus the percentage of the Detractors.
Let us look at an example for clarity sake: if you have ten total users, five of them are Promoters (gave a score of nine or ten) and three of them are detractor (gave a score of six or less), than your NPS Score is 50% - 30% = 20.
The idea behind the Net Promoter Score is a very simple, yet powerful one: sum the users who are happy and will promote your service, but detract those who are unsatisfied with it. The Neutrals will not really matter as they are indifferent to it.