What is the difference between filing Head of Household and filing married filing separately?

Married Filing Separately is somewhat penalized as you get the single Standard Deduction and you are disqualified from getting any most tax credits like Earned Income Credit and the Child Tax Credit. However, if you are married on December 31st of the tax year, you are required to file either Married Filing Joint or Married Filing Separately. The only exception to this is if you are legally separated by a Court Judge and have been for the last half of the tax year or more.