If you have already entered your Form W2 and there was state income taxes withheld, TurboTax automatically includes this as part of your itemized deductions.
Beginning on your 2018 Tax Return, you can only deduct a maximum of $10,000 for the combination of State, Local, Property, and Sales Tax deduction.
For more information on this new limitation, check out this TurboTax FAQ: How Will New Tax Legislation Affect My 2018 Tax Return?
