CAT percentile is calculated based on the no.of Candidates who appeared for the exam and no.of Candidates who scored lesser than you. For example, if you have scored 50 percentile it means that you have performed better than 50 percent of the Candidates who appeared for the exam. Now CAT has negative marking which means every wrong answer takes away a certain score. But unanswered questions will not have any impact. And CAT percentile is calculated using the formula: P=(R*N)/100, where P is percentile, R is Rank of the Candidate based on the CAT score and N is the no.of Candidates who appeared for the exam. Now you have not answered any question which means you will have no percentile both in sectional cut offs and overall cut offs. You will be assessed on your performance in the exam. But of you do not perform the exam at all, you will not be assessed on nothing. But we wonder if you will be able to submit the paper without attempting any questions because the Sysytem would not allow you to submit a blank paper.