CPT requires a job offer OPT does not require a job offer
CPT requires enrollment in an internship class in which on-the-job training is required and for which course credit is received. 
Student must be enrolled in the internship class at the same time they are working
OPT does not require you to enroll in an internship class
CPT authorized during the summer or winter would require the student to pay summer & winter tuition OPT does not require the student to pay for class registration, but U.S. Citizenship and Immigration Services (USCIS) requires a filing fee (it is $410 as of December 2019)
CPT is authorized for a specific employer for work related to student’s major field of study OPT allows work with ANY employer based on the student’s major field of study
CPT is authorized by OIP within 5 business days OPT is authorized by USCIS in 90 - 120 days (after preliminary processing by OIP)
CPT work permit is granted on the I-20 (page 3) OPT work permit is called the EAD (Employment Authorization Document)
CPT may only be issued for work before graduation OPT allows for employment both before and after graduation

CPT usually does not affect OPT as long as CPT is authorized for less than 12 months of full-time employment (more than 20 hours per week). Part-time CPT (20 hours per week or less) is never deducted from OPT. 

NOTE: if you work total 4 months of full-time CPT, you will still have 12 months of OPT

OPT authorized part-time (20 hours or less per week) is deducted at half-time rate, but full-time OPT (more than 20 hours per week) is deducted at full-time rate from the 12 months of OPT. 

NOTE: if you received 6 full-time months of OPT before graduating you will only have 6 months of OPT left after graduation


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