I just opened an HSA in February of this year (and was eligible for all of this year and last year).
I personally made contributions, using online banking, before April 15th that I claimed using Form 8889 when filing my taxes.
I realized that I did not specifically tell my HSA bank to apply the contributions to the prior tax year.
How can I remedy this?
You have to tell the bank at the time you made the contribution, that it is designated as a prior year contribution. This may be as simple as a drop-down menu in online banking, or you might have to mail a check with a special form, depending on the bank. You can't fix it retroactively.
First you need to file an amended return for 2017 that removes the contributions, adds them back to your taxable income, and pay the tax.
Then, since this contribution is official a 2018 contribution, it is applied to your 2018 limit. If you have ended up contributing too much for 2018, you have to make a "withdrawal of excess contributions". This also requires a special form or procedure, it is not a normal withdrawal. You will report the withdrawal of excess contributions on your 2018 tax return and they will be included in your taxable income.
You have to tell the bank at the time you made the contribution, that it is designated as a prior year contribution. This may be as simple as a drop-down menu in online banking, or you might have to mail a check with a special form, depending on the bank. You can't fix it retroactively.
First you need to file an amended return for 2017 that removes the contributions, adds them back to your taxable income, and pay the tax.
Then, since this contribution is official a 2018 contribution, it is applied to your 2018 limit. If you have ended up contributing too much for 2018, you have to make a "withdrawal of excess contributions". This also requires a special form or procedure, it is not a normal withdrawal. You will report the withdrawal of excess contributions on your 2018 tax return and they will be included in your taxable income.
Since the bank will not file a form 5498-SA for 2017 showing 2017 contributions, the IRS will bill you for the tax if you don't correct it, since they will see the form 8889 with no matching form 5498-SA.
Elaborating on the nature of the contribution, by default the HSA custodian must treat and report the contribution as a current-year contribution unless you explicitly indicated that the contribution was for the prior year by whatever method they require for making a prior-year contribution. Since it's now well past the deadline for making an HSA contribution for 2017, it's too late to treat the contribution you made as anything other than a contribution for 2018.
Can I retroactively file form 8889 for 2017? I have the right 5498-SA for 2017 but didn't know about the 8889 form so never got the tax back
Form 8889 is automatically generated by the tax software if you either (a) withdraw money from an HSA, or (b) contribute money to an HSA, or both.
If you made contributions in 2017 by payroll deduction, they are already reported. If you made out-of-pocket contributions for 2017 (including contributions made before April 15, 2018, if they were specifically designated as "for" 2017), and did not report them, you can file an amended 2017 tax return to take the deduction.
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