For your federal tax return, you can file Head of Household if you paid more than half the cost of maintaining a home for a qualifying person. A qualifying person for Head of Household status has to be related to you. For that reason, your partner wouldn't be a qualifying person for Head of Household. You would need to file Single for federal tax purposes.
For the state return, when you're in a registered domestic partnership, you must file using the same filing status as married couples. You can only file as Head of Household if you and your partner lived apart for the last six months of the year and you paid more than half the cost of maintaining a home for you and your child.
If you don't meet the qualification of Head of Household, you'd file either Married Filing Jointly or Married Filing Separately. It's important to note that since California is a community property state, your partner may be considered to have earned half of your income. If you file Married Filing Separately, you and your spouse would need to split your community income and you would both file tax returns.
Based on the above information, your filing status would be:
- Federal: Single
- California: MFJ/MFS
