You must be in F-1 status for one year to receive OPT. There are 2 categories of OPT: Post Completion and Pre-Completion.
Post Completion: Following graduation, F-1 international students are allowed to work full time for up to one year to gain work experience in their field of study before returning to their home country.
STEM OPT: In April 2008, USCIS published a regulation allowing F-1 students in STEM: Science, Technology, Engineering, and Mathematics fields to apply for an additional 17 months of OPT, beyond their initial 12 months. To qualify for the STEM OPT extension, a student must be engaged in an authorized OPT based on graduation from a program in the acceptable STEM field. The student must also be working for or have a job offer from an employer that is enrolled in the E-Verify system. Detailed information can be found at www.ice.gov/sevis/stemlist.htm
Pre-Completion: F-1 students can obtain OPT prior to graduation. They can work 20 hours a week while classes are in session and 40 hours a week during holiday and vacation periods. The amount of time used under Pre-Completion OPT is deducted from the students Post Completion OPT.
J-1 Academic Training (AT)
J-1 students may work under Academic Training following graduation for up to an 18 month period. They may also engage in AT for 20 hours a week while in school; 40 hours during holidays and vacation period. J-1 students should discuss the procedures for obtaining AT with their International Student Advisor (J-1 Responsible/Alternate Responsible Officer).