Can I claim my 2017 HSA contributions on my 2018 taxes?

[Opus 17]

Contributions made in 2017 must be reported on a 2017 return.  This includes contributions made before April 15, 2018 that you told the HSA bank were to be designated for 2017.  Contributions made in 2018, either before April 15 that were not specially designated, and anything after April 15, would be reported on your 2018 return.

2017 contributions made through your employer (including free money from your employer as well as your own payroll deductions) should be reported in box 12 of your W-2 and you automatically got the deduction when you entered your W-2.  If you made extra, after-tax contributions directly to the bank and forgot to report them, you can file an amended 2017 return.

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