The "6 month rule" essentially says you must stop contributing to an HSA account 6 months before you start your Medicare Part A plan. According to this Time article, it may be the case that the penalty is not enforced:
In fact, the IRS rules say you need to stop contributions six months before Social Security benefits begin, although I’ve never heard from anyone who lost tax benefits or was hit by an IRS penalty for such contributions.
Strangely, I can not find the "IRS rules" that the article links to, only this:
Enrolled in Medicare. Beginning with the first month
you are enrolled in Medicare, your contribution limit is
Example. You turned age 65 in July 2016 and enrolled
in Medicare. You had an HDHP with self-only coverage
and are eligible for an additional contribution of
$1,000. Your contribution limit is $2,175 ($4,350 × 6 ÷ 12).
Perhaps the reason the penalty is not enforced is because according to the IRS the 6 month rule doesn't actually exist? In other words, you were still legally covered by an HDHP until a certain date and were therefore eligible to make HSA contributions until that date. The fact the Medicare back dates coverage 6 months simply means you potentially had double coverage, but doesn't change the fact that you had a valid HDHP at the time the HSA contributions were made.
Note that even if you wait the 6 months, you may still need to undo any contributions which are more than 1/4 year's worth of eligibility (if you have had more than that this year already). Beyond that, if there is a penalty which is enforced, it means the "excess contributions" (the first 1/4 year's worth) would become taxable income AND you would pay an additional 6% excise tax.
So, I believe your options come down to this:
- If you are concerned about the the penalty, you could reverse the contributions made during the last 6 months and treat them as if they did not happen.
- You could wait out the 6 months and not have to worry about the penalty.
- You could assume the penalty isn't enforced and move forward.
My guess is that the amount you will receive in SS will more than make up for the difference in possible penalty you will pay, so I would probably lean towards option 3. However, if you are approaching a birthday, it might make sense to wait it out as each year you defer you increase your payment for the rest of your life. (Though you'll want to look into whether the 6 month rule means you have to wait until you turn 66.5 before starting benefits.)