Updated July 2026 · Reviewed by the CoverageCo team
Your Initial Enrollment Period runs seven months — the three months before your 65th birthday month, that month, and the three months after. Enrolling before your birthday month starts coverage with no gap. If you have coverage through active employment, you may be able to delay Part B penalty-free.
Key takeaways
- Sign up in the three months before your birthday month so coverage starts the month you turn 65.
- Late penalties for Part B and Part D are permanent — they last as long as you hold the coverage.
- COBRA and retiree coverage generally do NOT protect you from the Part B penalty. Only active employment coverage does.
- Review your plan every fall. Formularies and networks change annually, and the notice looks like junk mail.
Your first window: the Initial Enrollment Period
Your Initial Enrollment Period is seven months long. It starts three months before the month you turn 65, includes your birthday month, and runs three months after.
Enrolling in the three months before your birthday month is almost always the right move, because coverage can begin the month you turn 65 with no gap. Waiting until after your birthday month can delay your start date, leaving you uninsured in the meantime.
If you're already receiving Social Security benefits before 65, you're generally enrolled in Parts A and B automatically and your card arrives in the mail. If you're not receiving benefits yet, nothing happens automatically. You have to sign up yourself, and this is where people get caught.
Still working at 65? Read this before you skip Part B
If you have real, current coverage through your own or a spouse's active employment, you may be able to delay Part B without any penalty and enroll later through a Special Enrollment Period.
The critical detail is that not all coverage counts. Employer coverage generally has to come from active employment, and at a large enough employer. COBRA, retiree coverage, and Marketplace plans typically do not protect you from the Part B penalty, even though they feel like real insurance. People routinely assume COBRA counts, and it's an expensive assumption.
Before you delay anything, confirm in writing with your employer's benefits administrator whether your coverage is creditable for Medicare. Then confirm it again with someone who does this for a living.
What the late penalties actually cost
These aren't one-time fees. They're permanent additions to your premium, and that's what makes them worth avoiding.
- Part B: the penalty is calculated for each full year you could have enrolled but didn't, and it's added to your premium for as long as you have Part B. It doesn't expire.
- Part D: the penalty accrues for each month you go without creditable drug coverage, and likewise lasts as long as you have drug coverage.
- The Part D trap is subtle. People who take no prescriptions often skip drug coverage entirely, then discover years later that the penalty follows them for life once they finally need it.
The yearly windows after you're enrolled
Once you're on Medicare, two recurring windows matter. Both fall in the same part of the year, and they're easy to confuse.
Medicare Open Enrollment runs each fall. During it, you can join, switch, or drop a Medicare Advantage plan or a Part D plan for the following year. This is when most people review their coverage.
There's also a Medicare Advantage Open Enrollment window early in the year for people already enrolled in an Advantage plan, allowing one change. And a range of Special Enrollment Periods can open after qualifying events like moving, losing other coverage, or changes at your plan.
For current dates, always check Medicare.gov — these are set by CMS and are the one thing you shouldn't take from any agency's website, including ours.
Why reviewing every year matters more than people think
Plans change annually. Formularies get reshuffled, networks shift, and a plan that fit you perfectly can quietly stop covering a drug you depend on. The letter announcing it is easy to mistake for junk mail.
Staying put is a decision, not a default. A yearly review of your plan against your current medications and doctors takes very little time and is the single highest-value habit in Medicare.
A licensed agent can run that comparison for you each fall at no cost. If your plan is still the right fit, that's a perfectly good outcome and you'll know it rather than hoping.
Common questions
What happens if I miss my Initial Enrollment Period?
You may have to wait for another enrollment window to sign up, which can leave you without coverage in the meantime, and a late enrollment penalty may be permanently added to your premium. If you think you've missed a window, get help right away — some situations qualify for a Special Enrollment Period.
Do I need Part B if I'm still working at 65?
It depends on your employer coverage. Coverage through active employment at a large enough employer may let you delay Part B penalty-free. COBRA and retiree coverage generally do not. Confirm with your benefits administrator before delaying.
Is the Part D penalty permanent?
Yes. The Part D late enrollment penalty is added to your monthly drug plan premium for as long as you have Part D coverage. It's calculated from how many months you went without creditable drug coverage after becoming eligible.
Can I change my Medicare plan at any time?
Generally no. Changes are made during specific windows — Medicare Open Enrollment in the fall, the Medicare Advantage Open Enrollment window early in the year, or a Special Enrollment Period triggered by a qualifying event such as moving or losing other coverage.