Do not enter into 2017 TurboTax any medical expenses incurred and paid in 2017 (or 2018) for which you will be reimbursed from your HSA in 2018. Enter these expenses into 2018 TurboTax instead.
(This is necessary because TurboTax reduces the amount of entered medical expenses to be reported on Schedule A, line 1 by the amount of HSA distributions. If you intend to be reimbursed from the HSA, the expenses must not be included on Schedule A, line 1. In the year that you are reimbursed from the HSA, the expense must be entered because TurboTax will subtract it back out. All of this only makes a difference if you will end up with a medical-expense deduction after subtracting 7.5% of AGI.)
Note that you can only reimburse yourself from your HSA for qualified medical expenses incurred after the establishment of your HSA. If your HSA was not established until 2018, you cannot reimburse yourself for the expenses incurred in 2017. The date on which you established your HSA is governed by state trust law; your HSA is generally considered established on the date that the HSA account is first funded by an HSA-eligible individual.
