Should I prorate my HSA contributions when my HDHP ran through 12/17, but my Medicare Part A 02/18 enrollment was effective retroactively to 08/17?

[BMcCalpin · Accepted solution]

The habit of the SSA backdating the start of Medicare coverage by six months may seem generous to the SSA, but it plays havoc with HSA owners.

The month that you went on Medicare (e.g., August of the tax year), you ceased to be eligible to contribute to your HSA. Note, however, it is the coverage on the first day of the month that matters; therefore, if your Medicare coverage started after August 1st of the tax year, then you were still under the HDHP for August.

Yes, even if you were still under the HDHP until December, you lost eligibility to contribute to your HSA in August (or September, depending).

During the HSA interview, TurboTax will ask "Did (you) have Medicare at any time in [the current tax year]?" Answer "yes" and on the next screen indicate which type of coverage you had for which months - Self or Family for January through July (or August), and Medicare for August (or September) through the end of the year.

[Edited 3/10/2020 2:27 pm CDT - made year-neutral]