Taken from here.

Partial Year Contributions If you establish an HSA by at least December of any year, your maximum contribution is the maximum amount (described above) for that calendar year. However, if you choose to discontinue the qualified plan any time in the next 12 month period, the maximum contribution will be prorated for the number of full months in which the qualified plan was in force. You will be charged tax on the funds that exceed the maximum, as well as a ten percent tax penalty.

Contribution Deadlines HSA contributions must be made for a specific year on or before the due date (without extensions) for filing tax returns for that year. So contributions must be made on or before April 15th or the date you file your taxes, whichever comes first.

If I open an HSA after Dec. 31, 2018, any contribution (in 2019) goes toward the 2019 contribution limit? But the contributions made during Jan. - April 15, 2019 can be deducted from my 2018 gross income?

  • I'm a little confused. What was the date, exactly, that you opened your HSA?
    – Ben Miller
    Jan 18, 2019 at 20:18
  • Hi @BenMiller sorry, there was a typo. It should've said contributions made during Jan.-April 15, 2019. And I'm looking into opening one before the April deadline, sometime this month or the next couple of months.
    – jed
    Jan 18, 2019 at 20:24
  • Okay, but I still want to know the date your HSA started. Was it December 1, 2018, or some other date in December?
    – Ben Miller
    Jan 18, 2019 at 20:26
  • It would be in 2019. Say today, Jan. 18, 2019.
    – jed
    Jan 18, 2019 at 20:26
  • Were you HSA-eligible (covered by a High Deductible Health Plan) during 2018?
    – Ben Miller
    Jan 18, 2019 at 20:28

1 Answer 1


Since you were HSA-eligible for 3 months in 2018, you are allowed to make an HSA contribution for tax year 2018. There are two ways to calculate your 2018 contribution limit: you can either use a prorated limit (3/12 of the standard limit), or you can use the last-month rule to contribute the full amount for 2018. See this answer for more information on what your HSA contribution limit is during a partial year.

You have until April 15, 2019 to make 2018 tax year contributions to your HSA. However, since you have not yet established an HSA, you may find that whatever financial institution you end up using for your HSA will not want to accept a prior year contribution for a tax year that you did not have an account with them. You'll need to ask the financial institution if they will allow you to make a 2018 HSA contribution if you don't open the account until 2019.

If and when you do make a prior year contribution during the months of January-April, you need to inform the financial institution and explicitly designate the contribution as a prior year contribution. They need to know which year the contribution is for, and it isn't automatic.

  • Upvote for this and for the linked answer on how to contribute to the previous tax year for HSA consideration. Also, check out the examples for the contribution testing period (irs.gov/pub/irs-pdf/p969.pdf - page 5-6 for 2017). It two concrete examples for you to consider if you use the last-month rule to contribute the max HSA contribution for 2018.
    – Allen
    Jan 18, 2019 at 20:42
  • This is great, thanks so much @Ben Miller for this answer and the linked answer. I think I will use the Last Month Rule in order to contribute the 2018 contribution max for my HSA. Called the institution, and they said that was fine.
    – jed
    Jan 18, 2019 at 21:12

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