Hello student, the AIIMS MBBS is an examination conducted in 4 shifts. It is an examination which decides the cut off on the basis of the percentile score of the candidate and not the actual marks scored in the exam. Percentile score is the score which is calculated by considering the performance of the student with respect to the performance of all the students appearing for the exam. For example, the students scoring higher marks in the respective subject ( eg. Physics) will be given higher preference. This is done for all subjects and the final or overall percentile is calculated. 

Therefore, the last rank and the respective percentile will give the cut off for that respective category and year. The cut off changes every year depending upon the difficulty level of the exam, the number of students appearing for the exam, also the marks obtained in each shift by the students to calculate  the percentiler score.

Therefore, the qualifying cut off percentage is 45% for OBC category and the corresponding percentile is 97.011. 

It is therefore, necessary to score maximum marks in each of the subject and each of the four shifts of the examination, to achieve a higher percentile.

Good luck. 

The AIIMS entrance test which will be held on the 25th and 26th May, 2019 has a difficulty level much higher than NEET UG. That is why many students who qualify in NEET are not able to clear AIIMS. But that doesn't matter much if you have already got a medical college through NEET. The cut-off ranks for OBC in various campuses of AIIMS according to previous years'is:

Delhi(236)

Bhopal(1516)

Patna(2048)

Jodhpur (958)

Rishikesh (1664)

Bhubaneswar (1543)