Hi Raghavan,
Earned leaves and others are calculated on a pro-rata basis, i.e., after each length of service, they shall be credited to the employee's account accordingly. For example, if we have a structure of 18 earned leaves in a year, then after every month, 1.5 leaves will be credited to the employee's balance leave. I hope this information helps you to resolve your query.
Regards,
Amit Seth.