Adjustment of status to immigrant, when do you lose your non-immigrant status?

As long as your non-immigrant visa has not expired, you can continue to work on that visa without obtaining an EAD card. You will lose your non-immigrant status when your adjustment of status application "I-485" is approved and you become a permanent resident.

While you can still continue to work for the same company while your I-485 is pending, it is a good idea to obtain your EAD card now, that way you have the flexibility to be able to work for another employer, if necessary.

What "Letter" is the non-immigrant visa status? Some letters have a limited scope of duration and work authorization, and even requirement to return home for 2 years (J) compared to others. You also, free of charge, after paying the current fee of the adjustment of status and biometrics portion of the immigrant petition or visa-- do not have to pay for the I-765 which would provide work authorization if approved while the adjustment is pending- if any doubt- may as well file for it, especially as if in conjunction with the I-485, has no filing fee. Also, if you plan to travel outside the US, also w/ no fee if in conjunction with the I-485, you must have advance parole or you can face losing the ability to adjust status inside the U.S. I-131 is the document, and Advance Parole is the travel section (more than one travel purpose is on the form). Anyone who has been in Overstay or Out of Status should NOT travel outside the US while the adjustment is pending, as such people face unlawful presence and/or visa violation bars. A person loses their non-immigrant status when it expires, the date on your I-94 white card that should be in your passport along with your visa, with a date stamped on which is your period of stay granted to you by the Border Patrol Officer who inspects your passport, visa, and purpose for the stay and records the POS on your I-94 card. That's the date that counts. When you are approved to be an immigrant, then you have changed from non-immigrant status- and if there is a gap, as long as you are an immediate relative of a US citizen, the overstay, if there would be one (again, then don't travel outside the US) would not prevent the adjustment.

The person will lose their NIV status when either they depart the US and return on advance parole or when the NIV status expires.