@Zoso7
if you apply for Medicare during your window, it will take affect the first day of the month that you turn 65, which is June in your case. So you are correct that your contribution limit is 5/12 of $7750 which is $3229, plus 5/12 your $1000 catch-up, which is $416, for a total of $3645.
It doesn’t matter when in the year you make the contributions, you could even make the contributions after June, but your total for the year can’t be more than that number.
because making contributions through your employer reduces your Social Security and Medicare tax, as well as your state and federal income tax, it is slightly better to make contributions through your employer, than to fund your HSA in another way.
