If you file as Married Filing Separate, your refund will not be taken for his back child support. His refund will be taken for the back debt. Although, with Married Filing Separate you will usually pay more tax on a separate return, the standard deduction is half of what a joint return is, you cannot take all the credits you may qualify for, for ex. You cannot take the earned income credit or the education credits, and some deductions and credits are reduced at income levels that are half those for a joint return, for ex. Child Tax Credit.
