Hey Deepti

First of all let me Congratulate you because this is indeed a very good score,every year the ranks vary based on the total number of candidates who have written the exam so based on the previous year's analysis, with this score your rank may be somewhere around 120-540.

To get an idea about previous years ranks and marks please check the link given below:

ttps://medicine.careers360.com/articles/neet-result-marks-vs-rank

Thank You

Hello, 

646 is a very good score with a very good scope of admission in one of the best  medical colleges in India. The rank in 2018 for 640-650 was in the range of 123 - 232 and in 2017 was 302-535. Therefore, looking at the previous year's ranking, it can be said that your rank will be less than 100 in the AIR system.

This is just an estimate and may be affected due to various factors like the difficulty level of the exam, number of students appearing for the exam, the tie breaking factor, number of students scoring same marks in individual subjects as well as Overall NEET marks, etc.

Good Luck!