Medicare Enrollment Periods Explained: Dates, Deadlines, and Rules

Medicare has several enrollment periods, and knowing which one applies to you can help prevent coverage gaps and late enrollment penalties.

Some determine when you can first sign up for Medicare.

Others let you change Medicare Advantage or prescription drug coverage.

Medicare Supplement Insurance (Medigap) has its own separate enrollment period.

This guide explains the major enrollment periods, when they happen, and what you can do during each one.

Medicare Enrollment Periods at a Glance

Here's how the six major periods compare, based on Medicare's enrollment rules.

Each period has its own eligibility rules, and not everyone can use every one.

Which Windows Fall on the Calendar Every Year?

Three of these periods repeat on the same dates every year.

• General Enrollment Period
• Medicare Advantage Open Enrollment
• Annual Open Enrollment

Your Initial Enrollment Period, Special Enrollment Periods, and Medigap Open Enrollment aren't shown because their dates depend on your own situation.

1. Initial Enrollment Period: Your First Opportunity

Your Initial Enrollment Period (IEP) is generally your first opportunity to sign up for Medicare Part A and Part B.

It lasts seven months: the three months before the month you turn 65, the month you turn 65, and the three months after.

When your Part A and Part B coverage starts if you sign up yourself around age 65:

If your birthday falls on the first day of a month, Medicare generally treats you as turning 65 in the month before, so your window starts one month earlier.

If you're already receiving Social Security or Railroad Retirement Board benefits before turning 65, you'll generally be enrolled in Part A and Part B automatically.

Otherwise, you'll typically need to sign up yourself.

For more on the two parts you're enrolling in, see our guides to Medicare Part A and Medicare Part B.

2. General Enrollment Period: January 1 – March 31

The General Enrollment Period (GEP) is for people who missed their Initial Enrollment Period and don't qualify for a Special Enrollment Period.

It runs from January 1 through March 31 each year.

If you enroll during this period, coverage generally begins on the first day of the following month.

You may also owe a late enrollment penalty.

For Part B, the penalty is generally an extra 10% of the standard premium for each full 12-month period you could have enrolled but didn't.

This penalty usually lasts for as long as you have Part B.

3. Special Enrollment Period: Qualifying Life Events

A Special Enrollment Period (SEP) lets eligible people enroll in Medicare or change coverage outside the usual windows.

The rules depend on the qualifying event and the type of coverage involved.

Leaving Employer Health Insurance

If you delayed Part B because you had group health insurance through your own or your spouse's current employment, you may qualify for an eight-month Special Enrollment Period.

It generally begins the month after the employment or the group health coverage ends, whichever happens first.

Other Events That May Qualify

Special Enrollment Periods for Medicare Advantage and Part D may also open when you:

• Move outside your plan's service area.
• Lose certain other health or prescription drug coverage.
• Become eligible for Medicaid or Extra Help.
• Lose coverage because your Medicare plan leaves your area.

The length of these enrollment periods varies.

Learn more about Medicare Special Enrollment Periods.

4. Medicare Annual Open Enrollment: October 15 – December 7

Medicare's Annual Open Enrollment Period takes place every year from October 15 through December 7.

This is when people with Medicare can review and change their Medicare Advantage or Part D coverage.

During this period, you can:

• Switch from one Medicare Advantage plan to another.
• Leave Medicare Advantage and return to Original Medicare.
• Switch from Original Medicare to Medicare Advantage, if eligible.
• Join, switch, or drop a stand-alone Part D prescription drug plan.

Changes generally take effect January 1 of the following year.

What You Can't Do During Annual Open Enrollment

Annual Open Enrollment does not give you the right to buy a Medicare Supplement policy without medical underwriting.

If you leave Medicare Advantage and want Medigap, you may need to qualify medically unless you have guaranteed issue rights or qualify under special state rules.

That's because Medicare Advantage and Medigap follow different enrollment rules.

5. Medicare Advantage Open Enrollment: January 1 – March 31

The Medicare Advantage Open Enrollment Period gives people already in a Medicare Advantage plan another chance to make a change.

It runs from January 1 through March 31.

During this period, you can make one change:

• Switch to another Medicare Advantage plan.
• Leave Medicare Advantage and return to Original Medicare, with the option to join a stand-alone Part D plan.

Your new coverage generally begins on the first day of the month after the new plan receives your enrollment request.

People who join Medicare Advantage during their Initial Enrollment Period may also make one change during their first three months with Medicare.

6. Medicare Supplement (Medigap) Open Enrollment

Medicare Supplement Insurance has its own enrollment rules.

Your federal Medigap Open Enrollment Period lasts six months and begins the first month you're both:

• Age 65 or older.
• Enrolled in Medicare Part B.

During these six months, insurance companies generally can't refuse to sell you a Medigap policy they offer or charge you more because of your health.

Can You Buy Medigap After Open Enrollment?

Yes, but your options may be more limited.

Unlike Medicare Advantage and Part D, Medigap has no nationwide annual enrollment period when everyone can freely change policies.

In most states, insurers can use medical underwriting after your six-month Medigap Open Enrollment Period ends.

However, federal guaranteed issue rights and additional state protections may allow you to buy or switch policies without medical underwriting in certain situations.

Learn more in Medicare's Medigap enrollment guide or our overview of Medicare Supplement Insurance.

What Happens If You Miss a Medicare Enrollment Period?

Missing certain enrollment periods can lead to penalties, delayed coverage, or fewer insurance options.

Not everyone who delays Medicare will owe a penalty.

For example, people who delay Part B while keeping qualifying coverage through current employment can generally enroll later without one.

Which Medicare Enrollment Period Should You Use?

The right enrollment period depends on your situation.

Want Medicare Supplement Insurance? Pay close attention to your six-month Medigap Open Enrollment Period and any guaranteed issue rights that apply to you.

Frequently Asked Questions

Final Thoughts

Medicare enrollment periods serve different purposes, and understanding the deadlines can help you avoid unnecessary penalties or gaps in coverage.

The most important step is figuring out which enrollment period applies to your situation before you make changes.

For official rules, you can also call Medicare at 1-800-MEDICARE (1-800-633-4227).

Enrollment rules and eligibility can vary based on individual circumstances and state protections.