Dear Shri Keshav,
Sec 2 of Payment of gratuity act defines wages
wages” means all emoluments which are earned by an employee while on duty or on leave in accordance with the terms and conditions of his employments and which are paid or are payable to him in cash and includes dearness allowance but does not include any bonus, commission, house rent allowance, overtime wages and any other allowance.
Gratuity calculators available on the internet work out Gratuity like in this link
Gratuity Formula for Calculation of Gratuity Amount in India
But many of the other calculators take Basic pay +DA as the base for working out.