can tax payers claim his girlfriend on his tax return.
Maybe. Maybe not. You are awfully light on details.
Exemptions https://apps.irs.gov/app/vita/content/globalmedia/dependency_exemptions_4012.pdf
Support https://apps.irs.gov/app/vita/content/globalmedia/teacher/worksheet_for_determining_support_4012.pdf
So a definite MAYBE
If his girlfriend is a Minor, maybe.
If he is a Minor, maybe.
Which tax preparation program are you using for this client's return?
