To calculate customer loyalty, you will use the customer retention rate (CRR) as a standard measurement. This will show the number of customers you have retained over a particular period. The CRR formula is ((E-N)/S)) x 100. - E refers to the number of customers at the end of a week/month/quarter or another period. - N represents the number of new customers you sold to or acquired during this period. - S pertains to the number of customers you had at the start of the period.