The calculation varies from company to company. Ideally it should be a sum of all employees who left during the calendar month ( irrespective of reason or voluntary/ involuntary attrition)
The calculation of Attrition % is : (Total attrition/ avg headcount ) * 100
Employee Turnover ration will be the number of employees leaving per 100 employees. So if there are 5 employees leaving in a 50 member company, the ratio would be 1:10
Hope that helps
krish
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