The UPSC grading system for the Mains examination is based on a detailed evaluation of written papers. Each paper is scored out of a maximum of 250 marks, except the optional subject, which includes both General Studies and the Essay papers. The total marks from the Mains examination determine a candidate's eligibility for the final interview round. The UPSC follows a moderation process to ensure fairness. Candidates must achieve a minimum cut-off score to qualify for the next stage, making each component of the examination critical for success.