Currently I measure and report on the number of leavers each month, and the headcount figures at the end of each month.

In order to turn this into more meaningful data, how do I turn this information into :
1. A YTD turnover figure and
2. A projected annualised turnover rate (based on 3 months data as that is all we have)?
e.g. at end of Jan I had 100 employees and 2 leavers for the month, in feb we had 105 employees and 1 leaver, and in March 109 employees and 4 leavers