First, did you really have HDHP (High Deductible Health Plan) coverage on 12/1/2016 (this qualifies you for an HSA)?
Many taxpayers inadvertently answer this question when they really don't have HDHP coverage (in which case, they should have answered "none").
Line 18 has to do with the "last-month" rule. If you don't (and didn't) have HDHP coverage, then the whole situation doesn't apply to you.
If you are getting an error message in the review about form 8889 and Line 18 and you DON'T have an HSA or HDHP coverage, then please do the following:
1. make a copy of your W-2(s) (if you don't have the paper copies)
2. delete your W-2(s) (use the garbage can icon next to the W-2(s) on the Income screen
*** Desktop***
3. go to View (at the top), choose Forms, and select the desired form. Note the Delete Form button at the bottom of the screen.
*** Online ***
3. go to Tax Tools (on the left), and navigate to Tools->Delete a form
4. delete form(s) 1099-SA (if one), 8889-T, and 8889-S (if one)
5. go back and re-add your W-2(s), preferably adding them manually
Continue with your return.
***If, on the other hand, you did have HDHP coverage on 12/1/2016, then go back to the HSA interview (Federal->Deductions & Credits->Medical->HSA MSA Contribution) and go to the end of the interview. You can do that by clicking on Done on Your HSA Summary - the next screen should be the December 1, 2016 question.***
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