Can I contribute to my 2017 HSA before 4/17/18 which I joined a HDHP in July 2017, but finally received my HSA account this week?

[dmertz · Accepted solution]

Yes, assuming that you can't be claimed as a dependent on someone else's tax return and you are not covered by any disqualifying health insurance or Medicare.

Being an eligible individual on December 1, 2017 allows you to make a full-year's contribution under the last-month rule, but if you fail to remain HSA-eligible throughout 2018 you'll have to pay a 10% tax on the portion of your 2017 HSA contribution that you would not have been eligible to make were it not for the last month rule.