1. Pre-completion OPT:
You may apply for this OPT, upon completion of one (1) year of program at the school. You can work part-time, while school in session. Also, can work full-time while the school is not in session (such as during summer). The usage of this pre-completion OPT can result in deduction on the amount of work authorization from one (1) year. For example, if you work 4 months on pre-completion OPT, your post-completion OPT will be deducted and result in 8 months of total OPT for non-STEM graduates.
2. Post-completion OPT:
For non-STEM graduates, Optional Practical Training (OPT) only lasts for one (1) year. It is advised to start the process of applying for OPT at-least 60-90 days in advance to graduation. Usually upon graduation, F-1 student has 60 days from program end date to leave the country or apply for another immigration benefit including applying for OPT or any other benefit that best suits his/her situation. If you apply late to USCIS for OPT purposes, you may lose the amount of work authorization.
For STEM graduates, initial Optional Practical Training (OPT) authorization of 1 year can be extended for another 2 years upon application to USCIS for extension purposes.
24 month STEM extension:
You need to employed by an employer who is enrolled in E-Verify and received an initial grant of OPT based on your STEM degree. Make sure to complete I-983 training plan form along with the supervisor signature.