The visa expiration date shown on your visa does not reflect how long you are authorized to stay within the United States. Entry and the length of authorized stay within the United States are determined by the Customs and Border Protection (CBP) Officer at the port-of-entry each time you travel.
The visa expiration date is shown on the visa along with the visa issuance date. The time between visa issuance and expiration date is called the visa validity. The visa validity is the length of time the person is permitted to travel to a port-of-entry in the United States.
You are not traveling to a United States Port of Entry; you are already present in the United Sates and a Custom Border Protection Officer at the time you arrived to the port of entry issued you an I-94 and stamped on your passport the length of time he authorized you to stay in the United States following inspection and admission.
You can legally stay in the United States until the expiration of your authorized period of stay. However, you will not be able to travel to the United States Port of Entry to seek a new admission unless your visa has been renewed by the American Embassy in your country of Nationality.
Sometimes understanding the difference between the visa expiration date and the length of time a person has permission to remain in the United States can be confusing. These are very different terms.
A U.S. visa in a person’s passport gives a foreign citizen permission to apply to enter the United States. A visa by itself doesn’t authorize entry to the U.S. A visa simply indicates that the person’s application has been reviewed by a consular officer at a U.S. Embassy or Consulate, and that the officer determined the person was eligible to travel to a U.S. port-of-entry for a specific purpose. The port-of-entry can be an airport, a seaport or a land border crossing.
At the port-of-entry, a U.S. immigration officer of the Department of Homeland Security (DHS) decides whether to allow the person to enter and how long the person can stay for any particular visit, as part of the Admission process. Only the U.S. immigration officer has the authority to permit a foreigner to enter the United States.