NOL Carryforward for Individuals - HELP

[ElizabethP47]

Situation:  I have a client that ran a trucking business for a number of years and in 2022 exited the business due to the economy.  Once calculated, he has a $19k NOL Carryforward.  During the time of trucking, he was single.  In 2023 he got married and now will be filing jointly.  In 2023 he worked only W-2 jobs.

According to 536, he can only claim 80% of the excess of taxable income computed without regards to the NOL.  What does the publication mean by "excess"?  I also understand that this computation can only be done on his income. not joint. 
I just need help with this computation.  Also, what is appropriate to attach as a statement that shows the facts of this NOL?

Thank you so very much, in advance, for anyone's help.

[ElizabethP47]

@Anonymous_ Yes, I understand.  I do use ProSeries but I am trying to guide my client on how to do it on their own without stepping out of bounds with my tax preparer obligations.  I need to understand the mechanics behind it myself before I go and try to explain it to anyone else.

Thank you for your help.

[ElizabethP47]

I had no clue.  Thank you!