Enrollment

When can you enroll in Medicare?

Medicare has several enrollment windows. Knowing which one applies to you helps you avoid gaps in coverage and unnecessary penalties.

Written by Kayla Price, Licensed Medicare Agent (NPN 18530055)

Quick Answer

The Medicare Initial Enrollment Period (IEP) is a 7-month window that begins 3 months before your 65th birthday month, includes your birthday month, and ends 3 months after. Missing this window may result in permanent late enrollment penalties.

Medicare Enrollment Periods Explained

IEP — Initial Enrollment Period

Your Initial Enrollment Period is a 7-month window centered on your 65th birthday: the 3 months before your birthday month, your birthday month itself, and the 3 months after. This is typically the first chance most people have to enroll in Medicare — seethe basics of Parts A, B, C, and D if you're still getting oriented. If you enroll in the 3 months before your birthday month, coverage generally starts the first of your birthday month. Enrolling during your birthday month or in the 3 months after can delay when your coverage actually begins, so earlier is almost always better.

SEP — Special Enrollment Period

A Special Enrollment Period is triggered by certain life events — most commonly, losing employer group coverage or moving to a new service area. SEPs let you enroll or change coverage outside the usual windows without waiting for the next general opportunity. If you're still working past 65, see how employer coverage affects your timing. Most SEPs tied to losing employer coverage give you an 8-month window to sign up for Part B, starting the month after the employment or coverage ends — whichever comes first.

GEP — General Enrollment Period

If you missed your Initial Enrollment Period and don't qualify for a Special Enrollment Period, the General Enrollment Period (January 1 – March 31 each year) gives you another chance to sign up for Part A and/or Part B. Coverage under the GEP generally starts the first day of the month after you enroll, which can mean a gap of several months without coverage — one more reason the IEP and SEP windows matter so much.

AEP — Annual Enrollment Period

The Annual Enrollment Period, AEP 2026, runs October 15 – December 7, 2026. If you're already on Medicare, this is your annual opportunity to switch Medicare Advantage or Part D prescription drug plans for Plan Year 2027 coverage. Any changes you make during AEP 2026 take effect January 1, 2027.

What Happens If You Miss Your Enrollment Window

Missing your enrollment window doesn't just mean waiting longer to sign up — for Part B and Part D, it can mean paying more for as long as you have that coverage. Understanding these penalties is one of the biggest reasons to plan your enrollment ahead of time rather than after the fact.

Part B late enrollment penalty

If you don't sign up for Part B when you're first eligible and don't have other qualifying coverage (such as active employer coverage), your monthly Part B premium can go up about 10% for each full 12-month period you were eligible but didn't enroll. This penalty is generally permanent — it applies for as long as you're enrolled in Part B, not just for a year or two.

Part D late enrollment penalty

If you go 63 or more days in a row without Medicare drug coverage or other creditable prescription drug coverage after your Initial Enrollment Period ends, you may owe a Part D late enrollment penalty. It's calculated as roughly 1% of the "national base beneficiary premium" for each full month you went without creditable coverage, added to your premium for as long as you have Part D coverage.

Late enrollment can cost you. Missing your Initial Enrollment Period and not having other qualifying coverage can lead to late enrollment penalties for Part B and Part D that may last for as long as you have that coverage. Visit Penalties to see how these penalties are calculated. You can also confirm your personal enrollment dates at Medicare.govor sign up directly through the Social Security Administration.

How to Enroll

There are a few different ways to actually sign up for Medicare once you know which enrollment period applies to you:

Online at SSA.gov — the Social Security Administration handles Medicare enrollment, and signing up online atssa.gov/medicareis usually the fastest option for most people.
By phone — call Social Security directly, or call1-800-MEDICARE (1-800-633-4227) for general Medicare questions and guidance on your options.
In person — you can visit a local Social Security office if you'd rather enroll or ask questions face to face.
With a licensed Medicare agent — a licensed agent can walk you through your enrollment timeline, explain Medicare Advantage vs. Medigap, and help you compare plans, generally at no cost to you.

Before you enroll, it's worth checking that you're not about to repeat one of the mistakes we see most often — see our Top 7 Medicare Mistakes to Avoid for the full list.

For a full breakdown of exactly how the Part B and Part D late enrollment penalties are calculated, see Medicare Late Enrollment Penalties: How to Avoid Them in 2026.

Frequently Asked Questions

What is the Initial Enrollment Period (IEP)?

The IEP is a 7-month window around your 65th birthday (the 3 months before, the month of, and the 3 months after) when you can first sign up for Medicare.

What is a Special Enrollment Period (SEP)?

A SEP lets you enroll or make changes outside normal windows because of a qualifying life event, such as losing employer coverage or moving.

What is the General Enrollment Period (GEP)?

The GEP runs January 1 through March 31 each year for people who missed their Initial Enrollment Period and don't qualify for a Special Enrollment Period.

What is the Annual Enrollment Period (AEP)?

AEP runs October 15 through December 7 each year. It's when anyone already on Medicare can change Medicare Advantage or Part D plans for the following year.

What happens if I miss my Initial Enrollment Period?

If you miss your IEP and don't qualify for a Special Enrollment Period, you'll generally need to wait for the General Enrollment Period (Jan 1 - Mar 31), and you may face late enrollment penalties for Part B and Part D.

How much is the Medicare Part B late enrollment penalty?

The Part B penalty adds about 10% to your monthly premium for each full 12-month period you were eligible but didn't enroll and didn't have other qualifying coverage. This penalty is generally permanent and applies for as long as you have Part B.

How do I actually sign up for Medicare?

You can enroll online at SSA.gov, by calling Social Security or 1-800-MEDICARE, by visiting a local Social Security office, or by working with a licensed Medicare agent who can walk you through your options at no cost to you.

Not sure which enrollment window applies to you? Take the Medicare Decision Style Quiz orschedule a consultation with a licensed insurance agent.

Next: compare your coverage options

Once you know when to enroll, it's time to understand Medicare Advantage vs. Medigap.

Continue to Coverage Options