The date on your visa is not the end of your permitted stay
Visa validity, admission and immigration status answer three different questions. Confusing them can turn an ordinary journey into a serious problem.
One journey, several decisions
A visa in a passport is easy to treat as the complete answer to a travel question. It is visible, carries a date and looks authoritative. But the visa is only one part of the record. The Department of State issues visas through its consular process; admission to the United States is a separate decision made at the border by the Department of Homeland Security. A valid visa allows a traveler to seek admission for the relevant purpose. It does not guarantee admission.
The practical consequence is that the expiration printed on the visa should not become your departure deadline by default. After admission, look at the actual admission record. A person can have a visa that remains valid for years while the authorized period for a particular visit is much shorter.
Read the admission record in its own right
The I-94 record may show an admitted-until date or a duration-of-status notation, often written D/S. A fixed date and D/S do not mean the same thing. D/S is connected to maintaining the conditions of the relevant status; it is not an unrestricted permission to remain indefinitely.
Consider a hypothetical visitor whose visa expires in December but whose admission record permits a stay only until an earlier date. The December date does not extend that visit. Conversely, a visa expiring during an otherwise authorized stay does not, by that fact alone, establish the departure date. These examples explain the distinction; they do not resolve an individual status question.
When the records do not agree
Keep a copy of the admission record alongside the passport and relevant approval notices. If a name, classification or date appears wrong, identify which agency issued the record before seeking a correction. A consular visa issue and a border admission error may need different channels.
For readers comparing temporary travel categories, the B-2 visitor classification provides category background. It cannot tell you how long your own admission permits you to stay. Where a deadline has passed, a petition is pending, or travel may affect an application, obtain qualified advice rather than applying an example from a blog to your case.