Calculating HSA and 6 month lookback, to stop contributions

[klingram]

I want to stop my HSA contributions before the 6 month lookback day, but I am confused about which day to count back from.  Is it 6 months before the requested date for Medicare to START, or is it 6 months before the day you APPLY (make the request)? If I request a Medicare start date of July 1, but I make that request on May 1 (2 months before Medicare actually starts), does that make the 6 months lookback start on Jan 1 of the retirement year, or do I have to back up an additional 2 months to November 1 of the previous year?

[Opus 17]

You need to know your Part A Medicare effective date.  That's when HSA contributions must stop.

If you apply to Medicare during your normal window (3 months before or after your 65th birthday), Medicare will be effective on the first day of the month in which you turn 65.  If you sign up after your 65th birthday, coverage will start 6 months before you apply, except that coverage can never start before your 65th birthday month.

I don't quite understand how you can apply in May and request a July 1 start date, unless July is your birthday month.  In that case there is no lookback period because the coverage can't start before your birthday month.  But if you delay signing up for Part A until you retire at age 67 (for example), Part A will be retroactive to 6 months before you apply or 6 months before you apply for social security benefits.  

[dmertz]

"You need to know your Part A Medicare effective date.  That's when HSA contributions must stop."

That's when eligibility ends.  You still have until the due date of your tax return to make the maximum HSA contribution based on the number of months of eligibility.

[klingram]

I did not apply for Medicare on my birthday, as I was (and am) still employed, but am anticipating retiring soon. I used a  May application date for a July 1 start date (day after retirement) as an example to illustrate a 6 month lookback from an (arbitrary) start date vs a 6 month lookback from an (arbitrary) application date. 

Thank you for confirmation that the date I need to pay attention to is 6 months before I apply, which will make a difference in when I needed to stop my HSA contributions ... or depending on my application and actual retirement timing, it will make a difference in my request for overpayment distribution from my HSA.