Your marital status is determined by your status on the last day of December 2005. From your information, your filing status is either married filing a joint return or married filing a separate return.
Married persons.You are married for the whole year if you are separated but you have not obtained a final decree of divorce or separate maintenance by the last day of your tax year. An interlocutory decree is not a final decree.
Exception.If you live apart from your spouse, under certain circumstances you may be considered unmarried and can file as head of household.
You may be able to file as head of household if you meet all the following requirements.
1. You are unmarried or “considered unmarried” on the last day of the year.
2. You paid more than half the cost of keeping up a home for the year.
3. A “qualifying person” lived with you in the home for more than half the year (except for temporary absences, such as school). However, if the “qualifying person” is your dependent parent, he or she does not have to live with you. See Special rule for parent, on this page, under Qualifying person.
You are considered unmarried on the last day of the tax year if you meet all the following tests.
1. You file a separate return.
2. You paid more than half the cost of keeping up your home for the tax year.
3. Your spouse did not live in your home during the last 6 months of the tax year. Your spouse is considered to live in your home even if he or she is temporarily absent due to special circumstances.
4. Your home was the main home of your child, stepchild, or eligible foster child for more than half the year.
5. You must be able to claim an exemption for the child. However, you meet this test if you cannot claim the exemption only because the noncustodial parent can claim the child using the rules
described in Special Rules for Divorced or Separated Parents under Exemptions for Dependents.
for additional information.
Let me know if you have any question.
Please note: This advice is provided with the understanding that all the relevant facts have been provided by you. Any change in facts might affect the advice given and hence may not be relied on in such cases.