We purchased a large boat in 2016 and did not deduct the FL state sales tax from our 2016 Federal return. Do we need to amend our 2016 or deduct from our 2018 return?

[JohnW15]

If you paid the sales taxes in 2016, you'll need to amend your 2016 return to claim the taxes as a deduction.  You can't claim taxes in a prior year on a current-year return.

Please see the TurboTax FAQ "How to amend (change or correct) a return you already filed," below, for instruction on how to amend your previously-filed 2016 tax return.

https://ttlc.intuit.com/replies/3288565