It is important to always know when your I-20 is expiring. You can not let your program end date on your I-20 pass if you still need more time to complete your degree. Otherwise, you will be in violation of your F-1 status.
The expiration date of your I-20 can be found in the third box of your I-20 in the section called "PROGRAM OF STUDY" on the first page.
The expiration date of your I-20 and your "program completion date" are not always the same date. Your "program completion date" is the day you meet your academic program requirements. Your 60 day grace period starts the day after you meet your degree/academic requirements.