The length of time for which you will be allowed to stay in the United States on a J-1 exchange visitor visa (a type of nonimmigrant visa) depends on the type of program you will be participating in and the dates of your planned participation. (For basic eligibility requirements, see A J-1 Visa to the U.S.: Who Qualifies?)
In order to obtain a J-1 visa, you will need to present the U.S. government with a Certificate of Eligibility, Form SEVIS DS-2019. This form will be given to you by the sponsor of your exchange visitor program. It will list the specific dates you are expected to be participating in the program.
Upon entering the U.S. with your J-1 visa, you will be authorized to remain only up to the final date indicated on the Certificate of Eligibility. USCIS regulations do, however, place maximum time limits on J-1 visas according to the type of program.
Most students may remain in the U.S. for the duration of their programs plus an additional 18 months of practical training employment. Practical training is any employment directly related to the subject matter of the student's major field of study. Remaining in the U.S. for the additional 18 months of practical training is at the student's discretion. Postdoctoral training is limited to 36 months minus any previously used practical training time. (See 22 C.F.R. § 62.23.)
However, students between the ages of 15 and 18½ who are participating in a high school exchange program (living with a U.S. host family or residing at an accredited U.S. boarding school) are limited to one year's stay. They are not allowed to accept U.S. employment, except at odd jobs such as babysitting or yard work. (See 22 C.F.R. § 62.25.)
Exchange visitors who are teachers, professors, research scholars, or people with specialized skills may be issued J-1 visas for no more than five years, plus 30 days in which to prepare to depart the United States. (See 22 C.F.R. § 62.20 and 22 C.F.R. § 62.24.)
International visitors whose purpose of visiting and participating in the program is to promote cultural exchange, such as those working in places like the cultural/ethnic pavilions of Disney's Epcot Center, may be issued J-1 visas for no more than one year, plus 30 days in which to prepare to depart the United States. People qualifying under this category may, alternatively, be eligible for Q visas. (See 22 C.F.R. § 62.28.)
Foreign medical graduates may be issued J-1 visas for the length of time necessary to complete their training programs, up to a usual maximum of seven years (with limited exceptions), plus 30 days in which to prepare to depart the United States. (See 22 C.F.R. § 62.27.)
Business and industrial trainees may be issued J-1 visas for a maximum of 18 months. (See 22 C.F.R. § 62.22(k).)
Interns are eligible for up to 12 months of J-1 status to work with a U.S. employer while in the midst of a degree program in their home country or within one year of graduation. (See 22 C.F.R. § 62.22(k).)
Au pairs who are between ages 18 and 26 may come to the U.S. on J-1 visas to live with and perform child care (but not do other housework) for U.S. families. Au pairs may work no more than ten hours per day, 45 hours per week, must be paid at least the minimum wage, and must attend an institution of higher education to earn at least six hours of academic credit. Not many agencies have been approved to issue Certificates of Eligibility for bringing au pairs to the United States. Stays are limited to only one year and cannot be extended. (See 22 C.F.R. § 62.31.)
If this program interests you, check the State Department website at https://exchanges.state.gov.
Visitors may be invited by the U.S. government to participate in exchanges that strengthen professional and personal ties between key foreign nationals and the United States and U.S. institutions. They may be issued J-1 visas for the length of time necessary to complete the program, but no more than 18 months. (See 22 C.F.R. § 62.29.)
Youth workers over the age of 18 coming to serve as counselors in U.S. summer camps may be issued J-1 visas for a maximum of four months. (See 22 C.F.R. § 62.30.)
Postsecondary students may use a J-1 visa to work and travel in the United States for a four-month period during their summer vacations. This must be arranged through DOS-designated sponsors. (See 22 C.F.R. § 62.32.)
Professors and other academics participating in short-term activities, such as seminars, workshops, conferences, study tours, or professional meetings, may be granted up to six months on a J-1 visa. (See 22 C.F.R. § 62.21.)
An exchange visitor may be allowed to remain in the U.S. beyond the limitations stated above if exceptional circumstances arise that are beyond the exchange visitor's control, such as illness or a similar emergency. Talk to your program adviser if something like this comes up, or consult an attorney.