Gratuity should be calculated on basic salary or gross salary?

As per Indian Law Gratuity is a lump sum payment to employee based on his Gross earnings (Basic+ DA) when he retires or leaves service. Under Gratuity Act, gratuity is payable even to an employee who resigns after completing at least5 years of service.

Gratuity is payable @15 days wages for every year of completed service. In the last year of service, if the employee has completed more than6 months, it will be treated as full year for purpose of gratuity.

In case of employees paid on monthly wages basis, per day wages should be calculated by dividing monthly salary by26 days to arrive at daily wages e.g. if last drawn salary of a person (basic plus DA) is Rs.2,600 per month, his salary per day will be Rs.100 (2,600 divided by100). Thus, the employee is entitled to get Rs.1,500 [15 days multiplied by Rs.100 daily salary] for every year of completed service. If he has completed30 years of service, he is entitled to get gratuity of Rs.45,000 (Rs.1,500 multiplied by30). 

As per UAE MOL law Gratuity is being calculated on Basic Salary (last given basic salary)

Gratuity should be calculated on the basis of the basic salary which is stated in the employment contract. If there is no particular contract,  it can be calculated on the basis of the last drawn salary .