As far as we pay the salary on a monthly basis, including Sundays and other holidays, the earned leave will have to be calculated on a monthly basis only. It may vary from company to company.
In the normal course, one day a month is given as earned leave, thus totaling 12 days per annum. Casual leave is also for 12 days in a year but cannot be carried over to the next year, whereas earned leave can be accumulated for up to 3 years. Sick leave is also calculated as one day per month and can be accumulated for 3 years.
In U.S. standards, the sick leave is for 5 days, and other leave (whether earned or casual) is for 10 days.