If you are a US taxpayer, then there may be a few things you can do by December 31. If you are above the standard deduction for 2017 and if you pay estimated STATE income tax and the last payment for 2017 taxes is due in January 2018, then moving up payment to December 2017 may save significant money if SALT taxes are not deductible in 2018. My accountant suggested that I may want to pay my 2018 estimated state tax in December 2017 (which is allowed in California) since that will be be deductible in 2017. If you pay your 2017 property tax in split payments in 2017 and 2018 it may pay to make the second payment in 2017 for the same reason. Additionally depending on whether you will be under the federal standard deduction in 2018 but over the standard deduction for 2017, you may want to make charitable contributions for 2018 and future years in 2017. There are Donor-Advisor Funds (Vanguard and Fidelity have them) where you can donate and get the charitable deduction immediately, but delay the actual destination and amount to a future year.
For example, if you advance your estimated state income tax payment from January 2018 to December 2017 and the payment is $10,000, if you are in 35% federal tax bracket, you will save $3500, assuming SALT deductions are ended for 2018. If not, you have lost only the interest on the money.
Larry (I am not a tax attorney or CPA - Others more knowledgeable may want to comment or correct.)
For example, if you advance your estimated state income tax payment from January 2018 to December 2017 and the payment is $10,000, if you are in 35% federal tax bracket, you will save $3500, assuming SALT deductions are ended for 2018. If not, you have lost only the interest on the money.
Larry (I am not a tax attorney or CPA - Others more knowledgeable may want to comment or correct.)