A visa in your passport issued by from a U.S. consulate does not determine how long you can remain in the United States. Therefore, you may stay in the U. S. beyond the expiration date of a visa as long as the visa document (Form I-20 or Form DS-2019) remains valid. Once the visa expires it will be necessary to apply for a new visa stamp, through the same process as your initial visa application, at a U.S. embassy or consulate when traveling outside the United States.
If your U.S. visa has expired and you travel outside the U.S., you must obtain a new visa before you return. Applying for a new visa usually requires several weeks so you must plan your travel accordingly. If you are from one of the countries now requiring additional name check/security screening or in a high technology or technologically sensitive field, you may be subject to processing delays of 4-12 weeks.
Applying for a visa in a third country
It is possible for most international visitors to apply for a new visa in a country that is not their home country. Be sure to follow all U.S. embassy guidelines for applying, and additional wait time is possible if security checks are needed.
If you plan to visit Canada or Mexico to apply for a U.S. visa, it is particularly important that you check the Web site of the U.S. consulate to which you will submit your application. You will find instructions about how to make the visa appointment. If you are from one of the countries now requiring additional name check/security screening or in a high technology or technologically sensitive field, you will want to think carefully about applying for a U.S. visa in a third country.