Hey,
Here is the retention rate formula:
% Retention Rate (RR) = 100 - [ {S - (UT + BT)} / AE x 100]
Where:
RR = Retention Rate
S = Total number of terminations from whatever cause (In effect, this means the total number of employees that have left the company for whatever reason)
UT = Unavoidable terminations (i.e. retirements or long-term illness)
BT = Beneficial terminations (i.e. sometimes those staff that do leave provide benefit to the company by virtue of leaving, for example, underperformers)
AE = The average number of employees working for the company during the same period as calculated; this should be any period of 12 months.
Hope you will find this useful.