My fiancé is currently supporting me and my daughter as I am on maternity leave. We are having a baby in a few short weeks. How would he fill out his W-4 for this year?

[aprilg1990]

He currently claims 0. He makes 80k a year but he supports me, my daughter, and soon our new baby. Should he claim 3? Would that make him owe money next tax season? 

[Hal_Al]

He should claim 4.  If your daughter lives with him all year, he can claim her as an other dependent (not as a qualifying child; $500 credit , not $2000). If you marry before 12-31-19, she becomes his qualifying child. A step child is the same as a natural child, for taxes. A child born during the year counts for the whole year

Yes, there's a slight risk of owing a little. 3 would be "safer".