Hi Naveen,

CAT score is calculated through the normalization process. It's the scoring and equating process which is used to follow fairness and equity in comparison of performances of the candidates across different test sessions. The scores of the candidates shall be subjected to a process of Normalization. The percentile represents the rank of the candidate relative to the rest of the candidates who appeared for the same exam. 

Around 2 lakh candidates appear for CAT exam. Imagine you answer all the 100 questions correctly. So, you would be obviously at the top which means 1,99,999 students are behind you. So, your percentile would be 1,99,999 divided by 2,00,000 multiplied by 100 i.e. 99.9995 percentile. 

To know more about CAT exam, visit - Tips for CAT Preparation

All the best.