Calculation of Monthly Leave on pro rata basis for SL & CL?

Dear All
I am residing in Gujarat and working in company where we are having 21 EL, 7 CL, 7 SL. Both SL & CL are calculated on pro rata basis. My question is how do we calculate monthly leave for both SL & CL.
If I calculate on pro rata basis, for August leave stands at 4.67 to which we considered as 4. Our salary calculation goes from 16th to 14/15th of the month. Now if I calculate for September 2017, shall I calculate for whole month or I have to consider 15th.
Also, please let me know, how do we calculate leave for September 2017 because the leave stands at 5.25 for the month.
Thanks & Regards

Why do you need to calculate CL & SL every month? It is annual leave. You may allow the employee to avail leave on prorata basis or full basis. If employee separates then only you have to calculate leave on prorata basis for the period s/he worked for & deduct salary for extra leave availed, if any. Can employee avail 4.67 days leave?
For simplicity your leave cycle & pay cycle be the same; this will make your life easier.