Head of houshold: Domestic partner, and child, with joint checking

Question

I am living with my domestic partner and our child, and she contributes about twice what I do into our joint checking account from which all bills are paid. Can she file as head of household? I think she's checking all the right boxes:

• unmarried, filing separately
• claiming a dependent
• effectively pays > 50% of household expenses

Does the joint account make this difficult to establish? This is not in a community property state, if that matters.

Edit: I'm wondering what kind of documentation would be necessary in an audit. For example, it seems possible that if our household expenses are low enough that I could pay >50% of them, as long as her income was going toward something else.

Answer 1

Since money is fungible¹, the joint account would make it easier to demonstrate that she pays more than half of the household expenses

That's because there's a 2:1 ratio going in, so there's a 2:1 ratio going out, even though which dollars "belong" to who was lost when they got combined.

¹ able to replace or be replaced by another identical item; mutually interchangeable.