You don't have to have a dependent claimed on your return in order to file as a Head of Household. You still may be able to file using the status even if your ex-spouse claims a child as a dependent.
Head of Household status can be claimed by the spouse who has custody more than half of the year. Typically, eligibility is determined by your custody agreement.
To use the Head of Household status you must meet a series of requirements, including:
-You maintain the household in which the child lives for more than six months out of the year, even if they are not claimed as your dependent
-You are unmarried at the tax year's end or married and have been living apart from your spouse for over six months
Additionally, you may also qualify for the Child and Dependent Care Credit as well as Earned Income Credit for those which lower income amounts, and other tax credits you normally claim.
Your ex-spouse, the noncustodial parent, may claim the dependency exemption for a child if you, the custodial parent, releases a claim to exemption. Also, the noncustodial parent may claim the child tax credit for the child if the requirements for the child tax credit are met.