In order to claim/deduct mortgage interest two criteria must be met.
1) You must have a legal obligation to pay it. If your name is not on the mortgage, then generally you don't have a legal obligation to pay it. But if you live in a community property state, that complicates things.
2) You must actually pay it.
All this is covered in IRS Publication 535, Chapter 4.
My wife and I for reasons withheld are filing separate returns.
Just be aware that when a married couple files separate, that *automatically* disqualifies you for quite a lot of deductions and credits you would otherwise qualify for if you filed joint. If you have dependents, then you will feel it big time.
So if you're filing separate because of qualified student loan payments, what you may save in reduced payments, you will pay to the IRS with the loss of quite a lot of deductions and credits. For one thing, when you file separate returns, the student loan interest reported to you on the 1098-E is *NOT* deductible.
