Hi,
Please note that the Privileged Leave/ Earned Leave are to be credited only after completion of the year in service. In case an employee joins in between you might calculate the leaves on pro rata basis and credit them along with other employees to keep the calculations easy and on one date, preferably 01 Jan.
As far as CL/SL are concerned the employees can avail them from the date of joining though it will be calculated on pro rata basis if the date is other than 01 Jan. If you have 6 CL for an employee in a year and the employee happens to join in March, his/her CL available would be [6/12x10] 5 where 6 is actual leaves available, 12 are the calendar months in a year and 10 is the number of months the employee is expected to work in that year. Likewise the SL can also be calculated.
PL in the above instance will be 12.5 [15/12x10]. 2nd year onwards all the leaves will be as per the company policy in full and only PL/EL can be carried forward others would lapse at the end of the calendar year.
Thanks and Regards