When can I apply for citizenship ?
5 years after I-485 approval or 5 years after receiving green card or 5 yrs after I-551 stamp
Thanks in advance.
Well, typically that is the date of I-485 approval.Count your 5 years from "Resident Since Date" on face of your GC.
You can apply 5 years minus 90 days after your "Resident Since" date -- unless you have reason to believe the Resident Since date is wrong.
For some people, the Resident Since date is obviously wrong, sometimes it's before their I-485 interview or even before the I-485 filing itself, so they have to use something else like the date on the I-485 approval notice.
That's weird.
Well, typically that is the date of I-485 approval.
That's correct. For most people who got GC through adjustment of status, the "resident since" date should be the date of the I-485 approval. There are some exceptions, e.g. for those who applied for adjustment of status based on their asylum status, the "resident since" date is backdated one year earlier than the I-485 approval date. For those who obtained GC through consular processing, the "resident since" date should be the date of initial entry into the U.S. on an immigrant visa. As jackolantern notes, sometimes the "resident since" date printed on the physical GC is incorrect because of various USCIS screw-ups. So one does need to exercise common sense in double-checking the "resident since" date.