What is your question about HSA contributions? This is a message forum, not live chat. You have to post all the details of your question and wait for someone to respond.

In 2021, prior to the deadline, I made an HSA contribution for 2020. I'm working on my 2021 return right now [filed an extension]; I'm using Turbo Tax Home & Business. In terms of the questions Turbo Tax asks re HSAs, and in terms of the IRS Form 8889, I have found no way to enter my HSA contribution for 2020. [I have no contribution for 2021 as I went on Medicare in Sept. 2020.

@eligible 

<<In 2021, prior to the deadline, I made an HSA contribution for 2020>>

that HSA contribution goes on your 2020 tax return.  Assuming you turned 65 in September, 2020 and you are single, your maximum 2020 contribution was $4550 * 8 /12 or $3033.  if you turned 65 prior to September, then the maximum contribution was even less than that.

<<I have found no way to enter my HSA contribution for 2020.>>

because it goes on the 2020 tax return and not the 2021 tax return. 

and you can not turn around and say, well then, that contribution in 2021 before the filing deadline was really a 2021 contribution.  Since you are on Medicare, you are inelgible to make HSA contributions in 2021.

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@eligible   for the 2020 tax year, the IRS permits HSA contributions to occur from January 1, 2020 until you filed (let's assume no extension).   Those contributions that occur from January 1, 2021 until you file can be declared as 2020 contributions and deducted from your 2020 income.  You make that declaration to the HSA administratorat the time you make the contribution. 

It doesn't mean that because you made the contribution in 2021 and declared them as 2020 contributions they are deducted from the 2021 tax return - it doesn't work that way.  is has to be deducted from the 2020 tax return.  Is this the confusion?