If you stay in the United States past the permitted date allowed by your entry visa (shown on your Form I-94 Arrival/Departure Record as created by U.S. Customs and Border Protection), you risk being removed from the Unites States (deported) at any time. Nevertheless, many people opt to overstay, hoping they will eventually be able to adjust status. (Adjustment of status is the process of applying for a green card without leaving the United States.) Unfortunately, a visa overstay can ruin their chances to adjust status and immigrate at all.
If you have no current known basis for a U.S. green card, then overstaying your visa in hopes that you will become eligible is a big gamble. Even if you were to become green-card eligible, your overstay might interfere with your ability to adjust status to U.S. resident, as discussed next.
If you are in fact eligible for a U.S. green card—perhaps because you're closely related to a U.S. citizen or permanent resident, or you have an employer willing to petition for you—that's great. But realize that not everyone who is eligible for a green card is also eligible to adjust status in order to get it. Most people—though not all—will have to return to their home country for the final part of the green card application process, which includes an interview with a U.S. government official at the consulate or embassy there. (See What Happens During Consular Processing?.)
That might not sound bad, until you realize something important about the grounds of inadmissibility in the U.S. immigration laws. If you stayed in the U.S. unlawfully for more than six months (180 days), when you get to your visa interview overseas the consular officer will (unless you fit into a narrow exception) penalize you by refusing to allow you back into the United States for three years. If you overstayed for a whole year or more, the penalty is ten years. This is what's called a ground of "inadmissibility."
Your only hope might be to apply for a "waiver" (legal forgiveness) based on the hardship that your U.S. citizen or permanent resident relatives would experience if you were denied a green card, but these waivers can be hard to get. (See, for example, Staying in the U.S. With the I-601A Provisional Waiver of Inadmissibility.)
People who can and do adjust status—that is, process their whole green card application without leaving the United States—do not face these penalties.
A few people are actually allowed to adjust status even after their visa has expired, such as those who:
But you shouldn't attempt to figure out your own eligibility to adjust status after an overstay without experienced legal help.
If your visa status is likely to expire before you can apply for adjustment of status, contact an attorney right away, before the overstay occurs. The attorney can help you find out whether an extension or renewal is possible in your visa category, or whether there's some other solution to the situation. Keep in mind, it might not be possible to remain legally in the country, at least in the short term.
If you have already submitted your Form I-485 and supporting forms and documents to U.S. Citizenship and Immigration Services (USCIS), and you have received acknowledgment that it has received and accepted it for processing, you don't have to worry about renewing your visa. Your status in the U.S. is legal while you wait for the interview at which your adjustment of status will be decided upon.
If you overstay a visa and then leave the United States, your record may be examined any time you apply for future visas. You can be denied based on your past history of late departures from the United States.
If you believe you might be eligible for a green card, but are nearing the expiration date on your permitted stay under the terms of a visa, or you have already overstayed, you'll definitely want to consult with an attorney.
The attorney can analyze your personal situation and tell you how long it's safe for you to remain in the United States, whether you can adjust status, and if not, whether you're likely to qualify for a waiver allowing you to get a green card through processing overseas (known as "consular processing").