Your visa is issued by a U.S. Consulate abroad and placed in your passport. A visa permits you to apply for admission to the U.S. The visa may expire while you are in the U.S., but your permission to stay in the U.S. remains valid. All international students (with the exception of Canadian nationals) who request F-1 or J-1 immigration status must have a valid F-1 or J-1 visa in their passport at the time of entry to the U.S. Your visa specifies the type of immigration status you will hold (F-1 or J-1), the date until which you may enter the U.S., and the number of times you may enter the U.S. before you must apply for a visa. The length of validity of each visa type is determined by an agreement between your home country and the U.S. government, and is not related to the length of your program of study. Please refer to the U.S. Department of State Visa Reciprocity Tables for more information.
ALTHOUGH F-1 VISAS MAY BE ISSUED BY U.S. CONSULATES UP TO 120 DAYS IN ADVANCE OF THE PROGRAM START DATE, U.S. IMMIGRATION REGULATIONS DO NOT PERMIT F-1 AND J-1 STUDENTS TO ENTER THE U.S. MORE THAN 30 DAYS PRIOR TO THE PROGRAM START DATE. If you currently hold a valid F-1 or J-1 visa, you will not be permitted to apply for a visa renewal until 30 days or less prior to your current visa's expiration date.
F-1 or J-1 visas cannot be obtained in the U.S. You must apply for a new visa in person at a U.S. consulate abroad. The validity period of your visa does not determine the length of time you may remain in the U.S. Your length of stay is determined by the completion date of your program that is indicated on Form I-20 or the DS2019. You are admitted to the U.S. for "duration of status," noted "D/S" on your I-94 card.