All I know for sure, is that your 2019 property taxes must be "assessed" (billed) in 2018 in order for you to deduct/claim them on the 2018 tax return. That's how it stands right now. But with some states enacting workarounds for the $10K limit, the IRS has put out differing notices that they are working on wording and legislation to deal with those workarounds. So until final legislation is enacted it's impossible to know what the tax implications will be "for sure" if you pay a 2019 tax liability, in 2018.
