An unmarried couple live together with their child. Each is a professional person with a comparable six-figure income. They own their home jointly and share all expenses. The child lives with them 100% of the time and all of the child’s expenses are shared equally. Both parent's names are on the child's birth certificate. Since they are not legally married, they cannot file a Married-Filing-Jointly tax return.
Assuming no other factors, how does the IRS determine which of them can legally file as Head-of-Household and which must file as single?
