If you itemize deductions, the amount you can write off for state and local taxes (SALT), including state income or sales tax and local property taxes, is limited in 2018 to $10,000 ($5,000 for married persons filing separately). Until now, there was no limit.
If you live in a high tax state, you likely won’t be able to deduct all of your SALT. Some states have enacted or are considering enacting workarounds to enable their residents to get a federal tax break for SALT payments. However, the IRS has already nixed one attempt. It’s unclear whether states will go back to the drawing board on this one.