NTA scores normalised scores and are based on the relative performance off all those who appeared for the exam in  one session. The marks scored are converted to a scale ranging from 100 to 0 for each session. NTA score indicates the percentage of candidates who have scored equal to or below a particular candidate in that session.  NTA score of a Candidate is calculated using the formula:

100 X Number of candidates appeared in the Session with raw score EQUAL TO OR LESS than the candidate/Total number of the candidates appeared in the Session

NTA score is not the same as the percentage of marks.