How is the "State and local taxes greater than $5,000" line on the 2018 Federal Tax Deductions calculated in TurboTax? What is it based on?

[JLP1]

On the comparison of deductions shown for my 2017 taxes and my 2018 taxes, the bottom line under Itemized Deductions there is a line shown as "State and local taxes greater than $5000." I'd like to understand what goes into this calculation. My taxes are very complicated this year and I need to understand what is going into this calculation so that I can insure my state taxes are being calculated properly. I am needing to divid my income and deduction among multiple states.

[StacyC]

There is a change from 2017 to 2018 for the amount you can deduct for state and local taxes (withholding, estimates paid to your state, property taxes, DMV fees, etc). For 2017 and before this limitation did not exist so you could deduct much more in state and local taxes, for 2018 either $10k or $5k is deductible, depending on your filing status. 

It sounds like your filing status for 2018 is Married Filing Separately and the limit for taxpayers with this filing status is $5,000. The worksheet is listing the full amount of these taxes that you entered, and then subtracting out the amount over $5,000 to get to your state and local tax deduction of $5,000. 

You can also visit this comprehensive article for more information about the changes from 2017 to 2018: 

https://ttlc.intuit.com/replies/6971774