When can I enroll in Medicare?
Your Initial Enrollment Period is seven months long: the three months before the month you turn 65, your birthday month, and the three months after. Enrolling in the three months before your birthday month is what starts coverage on the first day of that month.
- Initial Enrollment Period: seven months, centered on your 65th birthday month.
- Born on the 1st of the month? Medicare treats your birthday as the previous month, and the whole window shifts a month earlier.
- General Enrollment Period: 1 January – 31 March, for anyone who missed their window.
- Annual Enrollment Period: 15 October – 7 December, to change Medicare Advantage or Part D for the following year.
- Still working past 65 with employer coverage? A Special Enrollment Period usually applies instead.
The seven-month window
The Initial Enrollment Period opens three months before your 65th-birthday month and closes three months after it. When coverage actually begins depends on where in that window you sign up: enroll in the three months before your birthday month and coverage starts on the first of your birthday month; enroll during or after it and coverage starts the first of the month after you sign up. Signing up early is what avoids a gap.
One detail catches people every year: if you were born on the first of a month, Medicare treats your birthday as falling in the previous month. Eligibility, the window and the coverage date all shift a month earlier.
If you are still working at 65
If you or your spouse are still working and covered by an employer group plan, you may be able to delay Part B without a penalty, then take a Special Enrollment Period when that coverage ends. This is where the rules turn on details that are easy to get wrong — the size of the employer matters, COBRA and retiree coverage do not count the same way active employment does, and the Part D clock runs separately from the Part B clock.
Getting this wrong is expensive and largely irreversible, so it is worth a conversation rather than a guess. There is no cost to ask.
The windows after your first one
If you miss your Initial Enrollment Period, the General Enrollment Period runs 1 January to 31 March, with coverage starting the month after you sign up — and a late-enrollment penalty may apply. Separately, the Annual Enrollment Period from 15 October to 7 December is when anyone already on Medicare can change Medicare Advantage or Part D plans for the coming year, and the Medicare Advantage Open Enrollment Period from 1 January to 31 March allows one further change for people already in an Advantage plan.
A qualifying life event — moving out of a plan’s service area, losing other coverage, a change in Extra Help status — can open a Special Enrollment Period at any time of year.
This is not a complete list of Special Enrollment Periods. Visit Medicare.gov for the full list.
Sources
- Medicare.gov — when to sign up U.S. Centers for Medicare & Medicaid Services
- Medicare.gov — costs and enrollment U.S. Centers for Medicare & Medicaid Services
Run the numbers yourself
Medicare date calculator
See your seven-month Initial Enrollment Period, your earliest coverage date, and your Medigap window.
Part D penalty calculator
See what going without drug coverage adds to your Part D premium — for as long as you keep it.