Which date needs to be taken into consideration for calculating Attrition?Date of Resignation or Date of Leaving?

Hi Team,
I work in education industry, i am working on Attrition report where we have cases like absconding,termination, left without serving notice period.
I have a doubt to calculating % to define for HR calender year.
Kindly help.

The attrition rate represents the trend of employees leaving an organisation for various reasons. When the frequency becoming frequent there is a cause of worry, especially when the educated, talented, trained & hard working lot creates such vacancies the organisation suffers and shoulder the burden of finding out suitable replacement. Since the attrition is the effect of vacuum created by the leaving employees it has to be 'date of persons actually not available to carry out the routine' work . However it's practical that an organisation should commence the process of finding the replacement from the date the resignation is reached the organisation. So the date should be reckoned from the date of resignation/termination irrespective of the notice period involved.

Dear Preethi,
Attrition is of two types viz., voluntary and involuntary. The cases of absconding, resignation you mentioned belong to the voluntary attrition while the other one of by termination at the instance of the employer belongs to the involuntary one. Yet another one coming to the natural termination of employment like retirement on attaining the age of superannuation.
Whatever its type be, the effective date is the actual date of separation on account of the termination of the contract of employment. In the case of resignation, it is the exact date of formal relief and not the date of submitting resignation or the effective date mentioned therein for the reason its acceptance can be postponed by the employer or the employee may withdraw it before it is accepted.