If your major is on the DHS official STEM OPT list, you may apply for two additional years of OPT. You will go through the normal OPT process to apply for your first year of OPT. Then you may apply for the two-year STEM extension near the end of your first year of OPT.
USCIS will accept your STEM extension application no more than 90 days before the end date of your regular OPT, as shown on your EAD. You can contact Calvin’s DSO about four months before your regular OPT ends to start the application process.
To apply for STEM OPT, you must be working at a company enrolled in E-verify. Check your company's website or contact their human resources department to check if your employer is enrolled.