The account retention rate is the counterpart of the churn rate. It allows you to define the ratio of retained VS lost customers over a certain period of time. You can calculate it on a Monthly or Yearly base depending upon your pricing model.
Account Retention Rate = (Total Number of Accounts at the end of the period / Total Number of Account at the beginning of the period) X 100
The Retention Rate is a critical metric that reflects how sustainable is your company and service. If the account retention is low, your business will slowly die even if you have decent customer acquisition results. When combined with your growth rate, this ratio also will enable you to forecast your recurring revenue.