Trying to ascertain if Turbo tax determines if tax filer has overlapping Medicare coverage and marketplace coverage (APTC), if the tax filer needs to pay back APTC for the overlaps months
TurboTax does not address it. Unfortunately, the current IRS Instructions don't really address it either. However, YES, the Law says that you do not qualify for the Premium Tax Credit if you are eligible for other insurance, such as Medicare.
Before you do anything, you first need to determine the actual situation.
You are disqualified for the Premium Tax Credit starting the month after you were approved for Medicare. In other words, if you received retroactive Medicare and/or the Medicare coverage started in the middle of a month, those months still qualify for the Premium Tax Credit. The disqualified months are only AFTER the month that you got approved.
The way that it would need to be reported is to enter zero in column B for the months of duplicate coverage. However, TurboTax will probably give you an error about that, and you would need to file by mail. You could also enter zero for column A instead of column B (it would give the same result) and it might not give you an error.