What is Customer Attrition?
Customer attrition is the loss of clients or customers. It is commonly presented as a percentage over a period of time. This metric is very important when measuring a company’s 
How to Calculate Customer Attrition?
Number of clients lost by the end of a period (clients at beginning of period- clients at end of period)/ Number of clients at the beginning of the period
Example: Company XYZ had 500 clients at the beginning of the fiscal year 2016; at the end of the year they had 400 clients, therefore 100 clients were lost.
100/500 = 20%
Company XZY’s attrition rate in 2016 was 20%.