Since there is a 10k cap with the (shameful IMO) tax plan, starting in 2018 you are are limited to 10k deductions for all SALT and property taxes.
Many jurisdictions are allowing pre-payment for property taxes (the plan prohibits SALT prepayment for itemizing), though it remains to be see if the IRS will allow you to actually reduce your AGI for 2017 for the property taxes. I plan on walking down to my treasurers office next Wednesday and cutting a big effin check. The question I have, and haven’t seen asked anywhere else is do you think this will fly for multiple years? I’m in the process of grabbing some scratch together to cover 18-19, but was considering putting in 20 as well.
Has anyone seen anything about multiple years? The IRS is woefully understaffed, so I think the odds are likely one could get away with this. AFAIK it’s not illegal, primarily because the new law doesn’t say you can’t do this.