Date of Admission is the 15th item in the Information About You part on Form I-90 (Part 1). Your Date of Admission is printed at the bottom of your Permanent Resident Card (green card). More specifically, your Date of Admission is located on the right of “Resident Since” on your green card. Enter this date in the form mm/dd/yyyy for month, day, and year respectively in the field 15, Part 1 on Form I-90.
Date of Admission is the date when you actually acquired permanent residentship or conditional permanent residentship in the United States. Note that the date when you first entered the U.S. may not coincide with the date you became a permanent resident.