The seven-month window, and why October birthdays trip people up

Your Initial Enrollment Period runs seven months, and almost nobody gets those seven months right on the first try.

The thing is, it isn't the seven months after your birthday. You count three months before your birthday month, then the birthday month itself, then three months after. So if you turn 65 in October, your window opened back in July and closes at the end of January — not April.

The month you choose changes your start date

If you sign up in the three months before your birthday month, coverage begins on the first of your birthday month. If you sign up during your birthday month or in the three months after it, coverage begins the month after you enroll.

That gap sounds academic until you're planning around a date. A retirement, a COBRA end date, a scheduled surgery, a spouse's plan changing at the end of the quarter — those all have their own calendars, and Medicare doesn't consult any of them. Enroll in the last month of your window and you can find yourself uninsured for a few weeks while one plan stops and the next one hasn't started.

The fix costs nothing at all: enroll early in the window rather than late.

What happens if you miss it entirely

There are two separate consequences here, and people tend to know about only one of them.

The first is that you may have to wait. The General Enrollment Period runs January 1 through March 31, and coverage starts the month after you sign up — so depending on when you noticed, that can be a long uninsured stretch.

The second is that Part B carries a late enrollment penalty: 10% added to your premium for every full twelve-month period you could have had Part B and didn't. And that penalty is permanent. It isn't a year of higher premiums or a fine you settle up — it rides your premium for as long as you have Part B, and it climbs when the standard premium climbs.

The exception that covers most people who delay

If you've had qualifying employer coverage the whole time, none of the above applies to you. You get a Special Enrollment Period of eight months once that coverage ends, with no penalty.

Whether your coverage qualifies is a real question with a real answer, and it turns on how many people your employer has. Retiree coverage and COBRA don't count as active employment, which surprises people who reasonably assumed any insurance counts as insurance.

What to do with this

If your birthday is inside the next several months, the useful next step isn't reading another explainer. It's writing down two dates — the month your window opened and the month it closes — and then, if you're still working, finding out your employer's headcount.

That second one is a five-minute call to HR, and it decides most of the rest. If you'd rather we worked through it with you, that's what the phone number is for. No charge, no obligation.