Legally separated is not a filing status. You either file married or single (possibly head of household if you have qualifying dependents). The IRS considers you unmarried if you have a legal separation agreement on the last day of the year. IRS Pub 501 has complete information about filing status to include information if you think you qualify as head of household.
https://www.irs.gov/publications/p501/ar02.html#en_US_2016_publink1000220721
In general, your filing status depends on whether you are considered unmarried or married.
Legally separated from your spouse under a divorce or separate maintenance decree.
Legally separated is not a filing status. You either file married or single (possibly head of household if you have qualifying dependents). The IRS considers you unmarried if you have a legal separation agreement on the last day of the year. IRS Pub 501 has complete information about filing status to include information if you think you qualify as head of household.
https://www.irs.gov/publications/p501/ar02.html#en_US_2016_publink1000220721
In general, your filing status depends on whether you are considered unmarried or married.
Legally separated from your spouse under a divorce or separate maintenance decree.