Section 7 of the payment of grauity Act 1972 will answer your query:
section 7.
(1) A person who is eligible for payment of gratuity under this Act or any person authorised, in writing, to act on his behalf shall send a written application to the employer, within such time and in such form, as may be prescribed, for payment of such gratuity– (2) As soon as gratuity becomes payable, the employer shall, whether an application referred to in sub-section (1) has been made or not, determine the amount of gratuity and give notice in writing to the person to whom the gratuity is payable and also to the controlling authority specifying the amount of gratuity so determined. 20[(3) The employer shall arrange to pay the amount of gratuity within thirty days from the date it becomes payable to the person to whom the gratuity is payable. (3A) If the amount of gratuity payable under sub-section (3) is not paid by the employer within the period specified in sub-section (3), the employer shall pay, from the date on which the gratuity becomes payable to the date on which it is paid, simple interest at such rate, not exceeding the rate notified by the Central Government from time to time for repayment of long-term deposits, as that Government may, by notification specify: PROVIDED that no such interest shall be payable if the delay in the payment is due to the fault of the employee and the employer has obtained permission in writing from the controlling authority for the delayed payment on this ground.]
In case notice is not sent to the employee with in 30 days or for delay if any on the part of the employer simple interst liability comes on employer.