Why do I need to put my spouse's info if we are not legally seperated or divorced yet, but are filing separately?

posted

Basically, it's because "the IRS says so". When a married couple files separate, if one of you itemizes deductions then you must both itemize, even if the itemized deductions of one of you is zero. Likewise, if one of you takes the standard deduction, then you must both take the standard deduction even if the itemized deductions of one of you is higher.

The IRS requires the spouse's name and SSN on the tax return so they can confirm you both take the same type of deduction.