When to Enroll in Medicare: A Guide to Your Enrollment Windows
Missing your Medicare enrollment window can mean higher premiums for life. Here is exactly when to sign up, what each window covers, and what to do if you are still working at 65.
Medicare enrollment has deadlines that, if missed, can raise your premiums permanently. The rules are not complicated once they are laid out plainly -- so here they are.
When does Medicare eligibility start?
You are eligible for Medicare the first day of the month you turn 65. If your birthday falls on the first of the month, your eligibility starts the first day of the prior month.
Most people qualify based on their own work history (or a spouse's). If you have paid Medicare taxes for at least 10 years, Part A (hospital coverage) is premium-free. Part B (medical coverage) has a monthly premium regardless.
What is the Initial Enrollment Period?
Your Initial Enrollment Period (IEP) is a 7-month window centered on your 65th birthday:
- 3 months before the month you turn 65
- The month you turn 65
- 3 months after the month you turn 65
Enrolling in the first 3 months of your IEP means your coverage starts the first day of your birthday month. If you enroll in your birthday month or after, coverage is delayed by 1 to 3 months.
The practical advice: enroll in the first 3 months of your window if you want coverage with no gap.
What if I am still working at 65?
If you (or your spouse) are actively working and covered by an employer group health plan with 20 or more employees, you can delay Part B without penalty. The group plan counts as creditable coverage.
When you stop working or lose that coverage, you get a Special Enrollment Period (SEP) that lasts 8 months. Enroll within those 8 months to avoid the late penalty.
Important: COBRA and retiree coverage do not count as creditable coverage for purposes of delaying Part B. If you leave your job and go on COBRA, you are in your SEP clock -- do not wait.
What is the late enrollment penalty for Part B?
If you miss your IEP or SEP and go without Part B for 12 or more months without creditable coverage, Medicare adds a 10% penalty to your Part B premium for every full 12-month period you went without coverage. The penalty is permanent -- it applies for as long as you have Part B.
Example: if you were uninsured for 2 full years, your Part B premium goes up by 20% -- for life.
What is the Annual Enrollment Period?
The Annual Enrollment Period (AEP) runs October 15 through December 7 each year. During AEP you can:
- Switch from Original Medicare to Medicare Advantage (or back)
- Change your Medicare Advantage plan
- Switch your Part D drug plan
Changes made during AEP take effect January 1 of the following year. AEP does not help you enroll in Medicare for the first time -- that is what your IEP or SEP is for.
What is the Medicare Advantage Open Enrollment Period?
If you are already enrolled in a Medicare Advantage plan, you have a second window: January 1 through March 31 each year. During this period you can switch to a different Advantage plan or go back to Original Medicare (and pick up a Part D plan). You cannot switch to Medigap during this window without medical underwriting in most states.
Enrollment timing at a glance
| Situation | Window | What you can do | |---|---|---| | Turning 65 | 7-month IEP | Enroll in Parts A and B | | Leaving employer coverage | 8-month SEP | Enroll in Part B without penalty | | Annual plan review | Oct 15 -- Dec 7 AEP | Change Advantage or Part D plan | | Already on Advantage | Jan 1 -- Mar 31 OEP | Switch Advantage plans or return to Original |
Common questions about Medicare enrollment
Can I enroll in Medicare online?
Yes. You can enroll in Part A and Part B through the Social Security Administration's website, by calling 1-800-772-1213, or at your local Social Security office.
What happens if I miss my Initial Enrollment Period?
You will have to wait for the General Enrollment Period (January 1 through March 31 each year), and coverage will not start until July 1. You will also owe a late enrollment penalty unless you qualify for a Special Enrollment Period.
Does my spouse's work coverage count for delaying Medicare?
Yes. If your spouse is actively employed and you are covered under their employer group health plan (with 20 or more employees), you can delay Part B without penalty based on that coverage.
Do I need to sign up for Part D separately?
If you have Original Medicare plus a Medigap plan, yes -- you need to enroll in a separate Part D drug plan. If you join a Medicare Advantage plan that includes drug coverage (most do), you do not need a separate Part D plan.
Have questions about your specific situation? Your Advocate can walk through your enrollment window, check whether your current coverage is creditable, and help you avoid the late penalty. Talk to an Advocate at no cost.