Turning 65 sets several clocks running at once, and they are not aligned. This is the order the decisions actually arrive in, and the two that cannot be deferred.
The seven-month window
The Initial Enrollment Period starts three months before the month you turn 65 and ends three months after it. Enrolling in the first three months generally means coverage starts without a gap; enrolling later in the window can mean waiting.
If you are already receiving Social Security retirement or disability benefits before 65, you are generally enrolled in Part A and Part B automatically and the card arrives. If you are not, nothing happens unless you act.
The first decision: are you still working?
This fork comes before everything else. If you or your spouse have health insurance through a current employer with 20 or more employees, you may be able to delay Part B without a penalty and use the eight-month Special Enrollment Period later. If not — retiree coverage, COBRA, a Marketplace plan, self-employment — you should generally take Part B now, because none of those protect you from the Part B penalty.
Get this wrong in the optimistic direction and you pay a percentage of the Part B premium for the rest of your life. The detail is in working past 65.
The second decision: Advantage or Original Medicare plus supplements
This one is time-limited in a way people are rarely told. The six-month Medigap Open Enrollment Period begins when you are 65 and enrolled in Part B, and inside it no insurer may refuse you on health grounds. In Florida, outside it, they can.
So choosing a Medicare Advantage plan at 65 is also a decision not to buy Medigap at the only moment it is guaranteed. That may well be the right call — it often is — but it should be a decision rather than a default. See Medicare Advantage vs Medigap.
The checklist, in order
- Three months before your birthday month. Confirm whether you will be enrolled automatically. If you are not drawing Social Security, assume you must apply.
- Establish whether your current coverage lets you delay Part B. Ask the employer or benefits administrator in writing. Twenty or more employees is the usual threshold.
- List your prescriptions and your doctors. Both drive the plan comparison more than the premium does. See checking doctors and drugs.
- Decide the structure before the plan. Advantage, or Original Medicare with a Part D plan and possibly Medigap. The structure constrains everything after it.
- Enroll, and diarise the Medigap window. It runs six months from the month you have both Part A and Part B.
- Check your Part D position even if you take few drugs. Going without creditable coverage accrues a penalty of 1 percent a month, and it is permanent.
Also on this site
Dated coverage of this topic, where the figures move year to year:
Frequently asked questions
When exactly does my Initial Enrollment Period start?
Three months before the month you turn 65. It runs for seven months in total, ending three months after your birthday month.
I am still working at 65. Do I have to take Medicare?
Not necessarily. If you have coverage through a current employer with 20 or more employees, you can usually delay Part B without penalty and use the eight-month Special Enrollment Period when the work or coverage ends. Retiree coverage and COBRA do not give you that protection.
Should I take Part A even if I am still working?
Most people can, because most people pay no premium for it. One exception matters: you cannot contribute to a Health Savings Account once you have Part A, so if you are funding an HSA, work out the timing before you enroll.
What happens if I do nothing at 65?
If you are already drawing Social Security, you will be enrolled in Part A and Part B automatically. If you are not, you will have no Medicare coverage, and a Part B late enrollment penalty will begin to accrue unless you qualify for a Special Enrollment Period.
Sources
- When can I sign up for Medicare? — Medicare.gov · read 2026-10-19
- When does Medicare coverage start? — Medicare.gov · read 2026-10-19
- Joining a plan — Medicare.gov · read 2026-10-19
This guide explains published rules and figures, with the source for each one. It is not advice about your own situation.