When married and fling separately, enerally the spouse that actually paid the expense or incurred the
deduction is the one able to claim it. For example, the spouse who
actually paid the mortgage interest and real estate taxes is the one who can deduct them. If the funds came from a joint account, typically the
expenses are split between them.
Note that the spouse claiming
the deduction must meet all the other requirements for the deduction on
his or her own, too. For example, you must actually be an owner of the
property to claim mortgage interest or real estate taxes paid. If your spouse is the only
owner of the property, then you don’t get a real estate tax deduction
when you file separately.
When married and filing separately both spouse's must either claim the standard deduction or must both itemize.
Another alternative
would be to file Jointly and also file Form 8379 Injured Spouse
Allocation. In most cases, you're better off filing a joint return and
including the injured spouse form. There are a number of tax credits that
are not available if filing separately. Form more information see: Publication 501,
Exemptions, Standard Deduction, and Filing Information
If you live in
a community property state, joint items such as income actually need to be
split evenly between the two of you. Filing separate returns in a
community property state can add up to be a real headache, see IRS pub 555 if
this applies to you: http://www.irs.gov/uac/Publication-555,-Community-Property-1.
Here are links to form 8379 and its instructions.
http://www.irs.gov/pub/irs-pdf/i8379.pdf
http://www.irs.gov/pub/irs-pdf/f8379.pdf
