What is churn rate?

There are several ways to calculate customer churn rate. One of the most practical ones goes like this:
Churn Rate = (Customers lost during the period/Total customers at the start of the period)*100
For example, you had 200 subscribers to your newsletter on March 1st. In March, 50 more people subscribed to your newsletter. However, the total number of your subscribers at the end of the month was 205.

Customers lost: 200+50-205=45
Churn rate: (45/200)*100=22,5%

Thus, the churn rate of your subscribers in March is 22,5%.
Each industry has different churn rate standards. However, a rule of thumb is that it's much cheaper and easier to retain customers rather than acquire new ones. Poor customer service and unsatisfying customer experience are among the main reasons why customers leave.
That's why companies use advanced CRM software, like Bitrix24, which helps to organize and monitor all interactions with potential or existing clients.