I oftentimes receive inquiries telling me that someone's visa status is about to expire and an application for extension of her/his authorized time in the U.S. is necessary immediately. When having the consultation I learn that although the visa is expiring, the person's status will remain valid for quite a while. The same occurs in the opposite circumstance: someone thinks that s/he may remain much longer in the U.S. because the visa in the passport has not yet expired, but upon further inspection it turns out that her/his status is about to expire or, worse, has already expired. Therefore, there is a great deal of confusion among visitors, students, workers, and other nonimmigrants regarding whether they are legally or illegally in the U.S.
This confusion occurs because of the difference between the validity of one's visa and the validity of one's status. While one normally requires a valid visa to enter the U.S., one requires a valid status to remain in the U.S. The validity of the visa, which is the document that is entered into a person's passport by a U.S. embassy or consulate abroad, is important at the time of entry to the U.S. The validity of the status, which is granted at the airport or border crossing or is otherwise extended or changed upon application while in the U.S., is important while remaining in the U.S.
I have posted a helpful chart below that summarizes the significant differences between a visa and a status:
