I'm in CA. My girlfriend and her kids are on my employee medical/dental benefits through domestic partnership...not 50% support. Paycheck has deductions. How do I file?

You cannot file as married on your federal tax return, but you can on the California return.

You cannot file as head of household if your dependents are not related to you. So, you would have to file as a single individual on your federal tax return.

Thanks for the tip.  Appreciate that. So for CA tax return, I can actually file as married (even though we are not)?  I do not support 50%, but just help cover insurance benefits for her and kids.  I just want to make sure since I have heavy deductions on my paychecks for Dom Prt s PreTx.

You must file as married-joint or married-separate on your California return if your domestic partnership is registered with the California Secretary of State. If you are not registered, however, then you cannot file as married.