Leaves given to employees are calculated on the basis of working days in a month.
Some companies give at the end of the month - some do it in the beginning of the year.
So, if an employee joins on 15th and you have 1-day leave for a month then 0.5 will be given on a pro-rata basis. (same calculation applies for yearly too)
For every 20 days of working 1 day of earned leave is mandatory for an employee - the law only says this and left to be decided as per the company and its policies.
Some companies split this into Sick - Annual - Earned - Casual etc which is as per their best practices and needs to attract and retain talent
We have blog on this: https://blog.greythr.com/leave-types-management-system
S&CE Karnatka: http://www.shram.org/uploadFiles/20131028113226.pdf