If one of you provided care in their home for a qualifying person, usually a dependent child (but there are some exceptions) then that spouse can file HOH and the other spouse files MFS. Or, both spouses file MFS.
Or, you can still file jointly if you agree to, that will usually have the lowest tax bill or largest refund, since many deductions and credits are reduced or disallowed when filing separately. But filing jointly depends on why you are living apart, and how well you get along despite that.
