I am filing a back years taxes (2015). I am entering my state withholding from my w-2 but turbotax is not reducing my federal amount owed. Am I missing something?

[DoninGA]

State income taxes paid during the year are an itemized deduction reported on federal Schedule A.  The total of all your Schedule A itemized deductions must be greater then the standard deduction for your filing status to have any tax benefit.

Standard deductions for 2015 

• Single - $6,300 add $1,550 if age 65 or older
• Married Filing Separately - $6,300 add $1,250 if age 65 or older
• Married Filing Jointly - $12,600 add $1,250 for each spouse age 65 or older
• Head of Household - $9,250 add $1,550 if age 65 or older