Medicare Enrollment Timeline: Every Deadline You Need to Know

Medicare enrollment deadlines aren’t suggestions — they’re hard cutoffs with real financial consequences. Miss the wrong one and you could face higher premiums for the rest of your life. That’s not an exaggeration. The Late Enrollment Penalty for Part B adds 10% to your monthly premium for every full year you were eligible but didn’t sign up. And it never goes away.

We hear from readers all the time who assumed Medicare would just “start automatically” or figured they could sign up whenever they got around to it. Some of them are now paying hundreds of dollars more per year because of a deadline they didn’t know existed.

This guide lays out every Medicare enrollment period, when it happens, what you can do during it, and what happens if you miss it. Our team member David helped both of his parents enroll on time, and the research he did for them is the foundation of this page. If you still have questions after reading this, email us at [email protected] — we’ll help you figure out your specific timeline.

The Enrollment Periods at a Glance

Medicare has five main enrollment periods, each serving a different purpose. Here they are in the order most people encounter them:

Let’s walk through each one in detail.

Initial Enrollment Period (IEP) — The Most Important One

Your Initial Enrollment Period is the seven-month window centered on your 65th birthday. It starts three months before your birthday month, includes your birthday month, and extends three months after.

Example: If you turn 65 in June 2026, your IEP runs from March 1 through September 30, 2026.

When Coverage Starts

Timing matters here. When your coverage begins depends on which month of the IEP you enroll:

• Months 1-3 (before your birthday month): Coverage starts on the first day of your birthday month
• Month 4 (your birthday month): Coverage starts the first day of the following month
• Month 5: Coverage starts two months after enrollment
• Month 6: Coverage starts three months after enrollment
• Month 7: Coverage starts three months after enrollment

The takeaway: sign up during the first three months of your IEP to have coverage the moment you turn 65. Waiting even one extra month delays your start date.

What to Sign Up For

During your IEP, you can enroll in:

• Part A (Hospital Insurance): Free for most people if you or your spouse paid Medicare taxes for 10+ years. There’s no reason not to sign up.
• Part B (Medical Insurance): Costs $185/month in 2026 (standard premium). This is the one with penalties if you delay without qualifying coverage.
• Part D (Prescription Drug Coverage): Standalone drug plan that works with Original Medicare. Also carries a late enrollment penalty.
• Medicare Advantage (Part C): An alternative to Original Medicare that bundles A, B, and usually D through a private insurer.
• Medigap (Medicare Supplement): Your Medigap Open Enrollment Period begins the month you turn 65 AND enroll in Part B. This is the only time you’re guaranteed acceptance regardless of health conditions.

What Happens If You Miss the IEP

If you miss your IEP and don’t qualify for a Special Enrollment Period, you’ll have to wait for the General Enrollment Period (January 1 – March 31) to sign up. Coverage won’t start until July 1 of that year. And you’ll face the Late Enrollment Penalty.

General Enrollment Period (GEP) — January 1 Through March 31

The GEP is the annual safety net for people who missed their IEP and don’t have a Special Enrollment Period. During these three months, you can sign up for Medicare Part A and Part B.

Key details:

• Coverage doesn’t begin until July 1 of that year — leaving you with a gap
• Late Enrollment Penalties will apply if you went without qualifying coverage
• Once enrolled in Part B, you can also sign up for a Part D plan or Medicare Advantage plan during the same period

The GEP exists as a fallback, but it’s not ideal. The coverage gap and penalties make it far better to enroll during your IEP or through a Special Enrollment Period.

Annual Election Period (AEP) — October 15 Through December 7

This is the window most Medicare beneficiaries use every year to review and change their coverage. Any changes made during the AEP take effect January 1 of the following year.

During the AEP, you can:

• Switch from Original Medicare to a Medicare Advantage plan
• Switch from Medicare Advantage back to Original Medicare
• Change from one Medicare Advantage plan to another
• Join a Part D prescription drug plan
• Switch from one Part D plan to another
• Drop Part D coverage entirely (though this could trigger a penalty if you go without creditable drug coverage)

What You Should Do Every October

Even if you’re happy with your current coverage, use the AEP to review your plan. Insurers change their formularies (lists of covered drugs), provider networks, and premiums every year. The plan that worked perfectly in 2025 might cost you hundreds more in 2026 because they dropped your medication from their preferred tier or your doctor left the network.

The Medicare Plan Finder tool at medicare.gov lets you compare plans side-by-side using your specific medications and preferred doctors. It takes about 20 minutes and could save you a significant amount of money.

Medicare Advantage Open Enrollment Period (MAOEP) — January 1 Through March 31

This period is specifically for people already enrolled in a Medicare Advantage plan. If you made a choice during the AEP that isn’t working out, or if you want to reconsider, the MAOEP gives you one more chance.

During the MAOEP, you can:

• Switch from one Medicare Advantage plan to another
• Drop your Medicare Advantage plan and return to Original Medicare (and sign up for a standalone Part D plan)

You cannot use the MAOEP to go from Original Medicare to Medicare Advantage — that’s only available during the AEP or an applicable SEP.

Changes made during the MAOEP take effect the first of the month after the plan receives your enrollment request.

Special Enrollment Periods (SEPs)

Life doesn’t always cooperate with scheduled enrollment windows. Special Enrollment Periods allow you to enroll in or change your Medicare coverage outside the standard periods when certain qualifying events occur.

Employer Coverage SEP

This is the most common SEP and the most important one for people still working past 65. If you or your spouse has employer-based health insurance through an employer with 20 or more employees, you can delay enrolling in Part B without penalty.

When that employer coverage ends (whether you retire, get laid off, or the employer stops offering coverage), you get an 8-month SEP to sign up for Part B. The clock starts the month after employment ends or the month after group health plan coverage ends, whichever comes first.

Critical note: COBRA coverage and retiree health plans do NOT count as employer coverage for this purpose. If you leave your job and go on COBRA thinking it protects you from the Part B penalty, it doesn’t. Sign up for Part B as soon as your active employer coverage ends.

Other Qualifying Events

• Moving out of your plan’s service area: You get a SEP to choose a new plan available in your new location
• Losing coverage involuntarily: If your plan leaves your area or drops your benefits
• Qualifying for Medicaid or Extra Help (Low-Income Subsidy): Opens a SEP to change Part D or Advantage plans
• Living in a nursing home or institution: You can switch plans once per calendar quarter
• Plan violation: If your plan misled you or violated its contract, CMS may grant a SEP

Late Enrollment Penalties — And How to Avoid Them

The penalties for late enrollment are real and lasting. Understanding them is the best motivation to enroll on time.

Part B Penalty

For each full 12-month period you were eligible for Part B but didn’t enroll (and didn’t have qualifying coverage), your monthly premium increases by 10%. This penalty applies for as long as you have Part B — meaning for life.

Example: You were eligible for Part B at 65 but didn’t enroll until 68. That’s three full years of delay. Your Part B premium in 2026 would be $185 + 30% = $240.50 per month. Every month. Forever.

Part D Penalty

If you go 63 or more consecutive days without creditable prescription drug coverage, you’ll pay a penalty when you eventually enroll. The penalty is 1% of the national base beneficiary premium ($36.78 in 2026) multiplied by the number of months you went without coverage.

Example: You went 24 months without Part D or creditable drug coverage. Your monthly penalty: 24 x $0.37 = $8.88/month, added to your Part D premium permanently.

How to Avoid Penalties

• Enroll in Part A during your IEP (it’s usually free)
• Enroll in Part B during your IEP unless you have qualifying employer coverage
• If you delay Part B for employer coverage, enroll during your 8-month SEP immediately when that coverage ends
• Keep continuous creditable drug coverage (Part D or an employer plan that’s as good as Part D)
• If your employer offers drug coverage, get a letter confirming it’s “creditable” — you may need it later

If You’re Turning 65 This Year

Here’s your step-by-step timeline:

Three months before your birthday:

1. Decide whether you need Part B now or can delay due to employer coverage
2. If enrolling, sign up for Part A and Part B at ssa.gov or your local Social Security office
3. Start researching Part D plans or Medicare Advantage plans
4. If choosing Original Medicare, get Medigap quotes during your Open Enrollment Period

Your birthday month: 5. Confirm your enrollment is processed and your Medicare card has arrived 6. Enroll in a Part D plan or Medicare Advantage plan if you haven’t yet 7. If buying Medigap, finalize your application during the open enrollment window

Three months after your birthday: 8. Verify all coverage is active and your providers accept your plan 9. Schedule your first Medicare Annual Wellness Visit 10. Set a calendar reminder for the next AEP (October 15) to review your choices

Missing a step isn’t the end of the world — but catching every deadline the first time saves you money and stress for years to come. If your situation is complicated (multiple employer plans, a spouse on different coverage, disability-based Medicare), consider calling your state’s SHIP program for free one-on-one counseling. They’re unbiased and funded by the government to help with exactly these decisions.

Have a specific timeline question? Email [email protected] and we’ll help you sort it out.