Yes, you can claim your mother if you provided more than half of her total support for the year (social security is not included in the support).
Your girlfriend's filing status is not relevant unless you share the same address. If both - your girlfriend and you - claim the Head of Household status while sharing the same address, you will need to
prove - if you are audited- whether you "conduct yourselves as separate households or one
household" and especially "whether each family acts independently of
each other in matters not related to the house."
Some factors
that would weigh in favor of there being two separate households but sharing
the same residence might include:
•Are there
separate telephone lines for each family? Separate utility bills?
•Do the
taxpayers maintain separate finances and separate bank accounts? Or do they
have a joint account or commingle funds?
•Does one
family contribute to the financial support to the other?
•Do the adult
taxpayers have separate bedrooms?
•Do the
children have separate bedrooms?
•Do the family
members give Christmas and birthday presents together or separately?
As you can see from these questions, the IRS will attempt to figure out whether the
taxpayers act as a family unit, or whether the taxpayers act as separate from
each other. The more that the two taxpayers act like they are in a family
relationship, the less likely the IRS will allow both taxpayers to claim head
of household.
