As we all probably know here by now :), the presumably soon-to-be-law tax bill does not deny a deduction for 2017 prepayment of 2018 property tax (like it does for income tax).
However, IIRC you can't (and could never) take a full deduction for arbitrarily pre-paid property tax. So if you for example (and to be silly) pre-paid 5 years worth of property tax in 2017 you would not be allowed to deduct that entire payment in 2017.
So what is the line? Can you take a deduction for a prepayment of what you'd "reasonably" expect you'd have to pay in all of 2018? Are you limited to only part of 2018? Are you limited to what you've actually received a bill for by the end of 2017? Are you limited to what's been assessed?
In my specific case, our town operates on a July 1-June 30 fiscal year. Sometime after July 1 they make an estimate as to what assessments will be and the August 2017 (FY2018) and November
2017 (FY2018) bills will be based on that estimate. Eventually they set the actual assessment and actual total FY2018 tax to be collected then the Feb 2018 (FY2018) and May 2018 (FY2018) bills will each just be half the difference between the total actual tax and the estimated tax they billed for in Aug and Nov).
Is my deductible prepayment limited to just paying off the rest of the FY2018 tax? Or can I deduct in full a prepayment for everything I'd reasonably expect to pay in calendar 2018?