Validity of my Registration

Hi Sir/Madam, I am a CA FINAL OLD syllabus student. I re-registered as a Final student as on 20.02.2013. I want to know that what is the validity of my registration and at what date should I renew my registration since I will be filling exam form for MAY2018 will I have to re-register my self before filling examination form or I can fill examination form and renew it after that. Please help me I am in very doubtful state. Thanks.