Turnover rate

Noun
1. the ratio of the number of workers that had to be replaced in a given time period to the average number of workers
(synonym) employee turnover, turnover
(hypernym) ratio

The number of total separations during the month divided by the number of employees who worked during or received pay for the pay period that includes the 12th of the month (monthly turnover); the number of total separations for the year divided by average monthly employment for the year (annual turnover)