Since my ex-wife still lives in my house and I pay 100% of our living expenses, can I claim her as a dependent? She could not live elsewhere.

[Hal_Al · Accepted solution]

Yes, if she lived with you all year and had less than $4400 of income. 

There are two types of dependents, "Qualifying Children"(QC) and Other ("Qualifying Relative" in IRS parlance even though they don't have to actually be related).  The Other dependent (qualifying relative) credit is worth (up to) $500 per dependent and is non-refundable.  That is, it can only be used to reduce an actual tax liability.

A person can still be a Qualifying relative dependent, if not a Qualifying Child, if he/she meets the 6 tests for claiming a dependent:

1. Closely Related (an ex spouse is not) OR live with the taxpayer ALL year
2. His/her gross taxable income for the year must be less than $4400 (2022).
3. The taxpayer must have provided more than 1/2 his support

In either case:

4. He must be a US citizen or resident of the US, Canada or Mexico
5. He must not file a joint return with his spouse or be claiming a dependent of his own
6. He must not be the qualifying child of another taxpayer