Your visa is only one of several “status documents” that describe your U.S. immigration status. If your visa is expired, it may mean you are out of status but it may not mean that at all.
The document that actually controls your U.S. immigration status is not your visa, but rather, your I-94 entry record. This used to be a little white slip that was stapled into a person’s passport. But now the I-94 is issued electronically, and you must download it from the website of the U.S. Customs & Border Protection (CBP: https://i94.cbp.dhs.gov/I94/#/home). Every time you enter the U.S., you should go to the website and print out your I-94. No matter what the date is on your H-1B approval notice, or on your visa, it is the I-94 that controls your stay in the U.S., so if there is an error, you need to get it corrected right away. You should also find a small, oval stamp in your passport with the entry date, status, and end date each time you enter the U.S., and the most recent stamp should match your I-94 record.
What if you didn’t leave the U.S. after your H-1B petition was approved? If your H-1B was approved as an extension of stay while you are in the U.S., a new I-94 record will be at the bottom of the approval notice (I-797A). It will say “Detach This Half For Personal Records” and it will have both the case number of your petition and your I-94 number from your most recent entry on it, along with your name, and “valid from” and “valid to” dates. It will also have your date of birth and your country of citizenship. By the way, you should NOT detach the I-94 record from the notice! Rather, you should keep the entire notice, intact, in your passport!
A visa, on the other hand, it like a “ticket” into the United States. If you are outside the United States, you need a “ticket” in, and that will be your visa. Your H-1B visa should have the same end date as your H-1B petition in most cases, and the end date of all three – visa, petition, and I-94 when you enter with that visa – should match. But: as long as you don’t travel outside the U.S., you don’t need a ticket back in. It’s like a museum: you pay the entrance fee, they give you a sticker, and as long as you don’t leave, you can stay until the end of the day.
For example: You came into the United States as a student on a student (F-1) visa. You then are hired by a U.S. company that petitions for H-1B status on your behalf, and your status changes on October 1, 2022 to H-1B. You have an approval notice that has the I-94 record at the bottom, and they both expire on September 30, 2025. But you don’t travel outside the United States. Your employer extends your status to September 30, 2028. You still don’t travel, but your I-94 covers your status until that date, even though your visa is long-expired, and you entered in a different status.
What if you must travel? Your parent falls ill, you decide to get married back home, or you really need to take your vacation time? If you leave the U.S., you MUST apply for a new H-1B visa at a U.S. consular office abroad, because you want to come back into the U.S. and continue to work in H-1B status. The new H-1B visa should have an end date that matches your H-1B approval notice, and when the border officer looks at your visa and approval notice, he should input the correct end date and status, so that the new I-94 record matches your visa and petition.
By the way, you should make sure your employer knows about your planned travel, and that their immigration attorney advises on any questions you have about applying for a visa. The procedure can change suddenly and without notice and is not the same in every country or at every U.S. consulate, so it’s best not to rely on what you did “last time” you applied for a visa.