as per Indian Act “The Payment of Gratuity Act, 1972” (open the link in IE or refer to this page for quick brief) every employer in India shall pay gratuity to an employee at the rate of fifteen days’ wages based on the rate of wages last drawn by the employee concerned for every completed year of service or part thereof in excess of six months.
Recently there has been amendment to the policy act (judged by Madras high Court) which states that employees who served a company for not less then 4 years and 8 months shall as well be paid the Gratuity in similar status to that of employees served for 5 years. Refer to RTI-India portal for more details.
Use the Indian-Gratuity-Calculator and note that whole of gratuity amount is free of all your IT Tax.