Failure to complete the testing period for the last-month rule does not create an excess contribution. It simply makes the portion of your 2022 contribution in excess of the amount that you would have been eligible to contribute without the last-month rule subject to a 10% extra tax. Because there is no excess contribution for 2022, you are not permitted to obtain a return of any of the 2022 contribution but must instead pay the 10% extra tax. 2023 TurboTax will automatically calculate and assess the 10% extra tax on Form 8889 Part III.
Because you will be covered on December 1, 2023, you are eligible to contribute the full annual amount for 2023 under the last-month rule. Because you only had coverage for 6 of the 12 months of 2023, if you make a full-year contribution for 2023 under the last-month rule but fail to remain HSA eligible throughout 2024 you will owe a 10% extra tax on 1/2 of the annual limit, assessed on your 2024 Form 8889 Part III.
