If you and your domestic partner live by yourselves, neither of you may file a return as a head of household. To qualify for that filing status, you must have a dependent living with you, and it can't be your partner. If you and your partner have a qualifying child or qualifying relative, you may have a shot.
Head of Household
To qualify as head of household on your Form 1040, you must be unmarried, pay more than half the cost of keeping up your home and have a qualifying person living with you for more than six months. When adding up your living costs, include rent, mortgage interest, property taxes, insurance, repairs, utilities and meals you eat at home. The amounts you pay for your education, transportation and medical treatment for you and your partner do not factor in.
A qualifying child can be a grandchild, stepchild, younger sibling, or a niece or nephew. Generally, your dependent must live with you more than six months out of the year -- the IRS allows exceptions for vacations or hospital stays -- and you must pay more than half his support for the year. The qualifications are similar to those for claiming a dependent exemption, but some dependents don't qualify you as head of household.
The IRS says that it's possible, at least in theory, for your domestic partner to be your dependent. If he makes less than the standard exemption and you provide more than half his support, you may be able to claim him in the qualifying relative category and take an exemption for him. He is not, however, a qualifying relative by head of household rules. If you don't have a qualifying dependent available, your only option is to take single filing status.
One or None
When you have a qualifying person in your home, you or your partner -- but not both of you -- may claim head of household status. In some cases, neither of you can do it: If your partner pays more than half the household expenses but you pay more than half the dependent's bills, neither of you meet the IRS qualifications. If you think the tax advantages are worth it, consider adjusting how you pay the bills so that one of you can grab the filing status.