To calculate your NPS, it comes down to asking one simple question to your customers:

“How likely is it that you would recommend our company to a friend or colleague?”

The respondent is then given a standard scale that ranges from 0 (not at all likely) to 10 (extremely likely). Based on how a customer responds, he/she is classified into one of three categories:
​Promoter (9-10)
​Passive (7-8)
​Detractor (0-6)

Source

Once each customer is classified into a respective category, your company’s Net Promoter Score can be calculated by subtracting the percentage of Detractors from the percentage of Promoters. It will be a number between -100 and 100.

As explained in Qualtrics’ blog:

Promoters are best described as your customers who are loyal and enthusiastic about your company and will continue buying and referring others. Promoter referrals fuel viral growth that you don’t have to pay for. The cutoff for Promoters is intentionally high at 9 to ensure that the customer is an exceptionally enthusiastic fan.

Passives are generally satisfied customers, but lack the enthusiasm seen in the Promoter group. A 7 or an 8 rating is no doubt impressive, but research has found that this group is vulnerable to competitive offerings and is therefore not immune to defection.

Detractors are a potentially dangerous bunch who are often unhappy and can diminish your brand through negative word of mouth. A customer who rates your company between a 0 and a 6 requires proactive outreach to resolve issues before damage is done.

To determine if your NPS is good, you need to compare it to the average in your industry. What is considered 'good' in one sector may be considered 'bad' in another, for example.

In summary, the Net Promoter Score can definitely help your business. By calculating and improving your NPS, you will increase your customers’ loyalty, generate more positive word-of-mouth and more referrals, which leads to more revenue and higher profits.

Most companies use modern tools to keep track and to improve their Net Promoter Score over time. It lets them automate the feedback process.