The Complete Guide to Medicare Open Enrollment 2026

Medicare enrollment has more windows, deadlines, and exceptions than almost any other insurance system in the US. Miss the right window by a month and you could pay a late enrollment penalty that lasts the rest of your life. Sign up too early in the wrong sequence and you could accidentally delay your drug coverage. Make a plan switch you didn't understand and discover in February that you can't undo it until next October.

These are real things that happen to real people every year.

The good news is that once you understand how the system is structured, it's actually pretty logical. There's a sequence to follow and specific windows for specific purposes. This guide walks through all of them—not just the headline AEP that insurance commercials scream about every fall.

Your Initial Enrollment Period (IEP) is the 7-month window centered on your 65th birthday month. It starts 3 months before you turn 65, includes your birthday month, and runs 3 months after.

So if your birthday is July 15, your IEP runs April 1 through October 31.

### When Your Coverage Starts Depends on When You Enroll

This is where the timing gets specific:

If you enroll in the 3 months before your birthday month: coverage starts the first day of your birthday month.

If you enroll during your birthday month: coverage starts the first day of the following month.

If you enroll in the 3 months after your birthday month: coverage starts 2-3 months after enrollment.

So enrolling early in your IEP gets you coverage faster. Someone with a July birthday who signs up in April gets coverage July 1. Someone who waits until September gets coverage November 1. Four months of gap matters if you need healthcare.

### Social Security and Automatic Enrollment

If you're already receiving Social Security benefits when you turn 65, you're automatically enrolled in Medicare Parts A and B—you don't need to do anything. Your Medicare card shows up in the mail about 3 months before your 65th birthday.

If you're not yet receiving Social Security (maybe you're still working or delaying benefits), you have to actively sign up. You can do it at SSA.gov, by calling Social Security at 1-800-772-1213, or in person at a Social Security office.

### The Part B Decision for Working People

If you have employer coverage through a large employer (20+ employees) when you turn 65, you have options. You can delay Part B enrollment without penalty because your employer coverage qualifies as primary insurance.

This matters because Part B costs $202.90/month in 2026. Some people with good employer coverage prefer to delay Part B to save that premium while still working. When you eventually leave employer coverage, you get a Special Enrollment Period to sign up.

Small employer (fewer than 20 employees)? Different story. Medicare becomes primary and your employer plan secondary. In that case, declining Part B could leave huge gaps in coverage.

The late enrollment penalties for Medicare are, frankly, brutal. They're designed to push people to enroll when first eligible. And they work—because the alternative is expensive.

### Part B Late Enrollment Penalty

If you didn't have qualifying coverage (employer insurance from a large employer, for example) and you didn't sign up for Part B when first eligible, you pay a 10% penalty for each full 12-month period you delayed.

Two years late? 20% penalty. Ten years late? 100% penalty, meaning you pay double the standard premium.

The penalty is permanent and is added to your monthly Part B premium for as long as you have Part B. In 2026, the standard premium is $202.90. A 20% penalty adds $40.58/month—every month for the rest of your life. Over 20 years of retirement, that's almost $10,000 for one avoidable mistake.

### Part D Late Enrollment Penalty

Miss the window to enroll in Part D and you pay 1% of the national base beneficiary premium ($38.99 in 2026) for every month you went without creditable drug coverage.

Six months without coverage: roughly $2.34/month penalty. Small but permanent.

Two years without coverage: roughly $9.36/month. Still small. But if you put off Part D for five years thinking "I don't take many drugs," that's a $23/month penalty every month going forward. Plus the standard premium on top. It adds up.

### What Counts as Creditable Coverage

You don't get penalized for gaps during which you had other creditable drug coverage. Your employer's drug coverage, most union plans, TRICARE, VA drug coverage (with caveats), and FEHB all typically qualify.

If you're leaving employer coverage, your plan administrator should provide a Notice of Creditable Coverage. Keep that document. You'll need it to prove you didn't have a gap.

### Part A Late Enrollment Penalty

Less common because most people get Part A free. But if you have to pay a premium for Part A and you don't sign up during your IEP, the penalty is 10% of the premium for twice the number of years you delayed. Miss two years, pay the penalty for four years.

Most people shouldn't have to worry about this.

This is the big one. The AEP—sometimes called the Annual Election Period—runs every year from October 15 to December 7. Changes made during AEP take effect January 1 of the following year.

What you can do during AEP:

### AEP Strategy: Don't Auto-Renew Without Checking

This is where I see people lose money every single year. Medicare Advantage plans and Part D drug plans can change their premiums, cost-sharing, formularies, and networks every January 1. Your plan sends you an Annual Notice of Change (ANOC) every fall—typically in late September—that details what's changing for the coming year.

Most people don't read it.

Then they spend January discovering their drug was removed from the formulary, their cardiologist left the network, or their premium jumped $40/month. And they have to wait until next October to fix it.

Read the ANOC. Compare your current plan against alternatives on Medicare.gov or by calling 1-800-MEDICARE. Take 30 minutes in October. It can easily save you hundreds or thousands.

This window is specifically for people already enrolled in Medicare Advantage. During the MA OEP (January 1 – March 31), you can:

You cannot use the MA OEP to join Medicare Advantage for the first time. That's what AEP is for.

Changes made during MA OEP take effect the first day of the month following your enrollment. Enroll in a new plan on February 10, coverage starts March 1.

### Why MA OEP Exists

It was created partly as a consumer protection measure. People who enrolled in MA during the fall AEP, then discovered in January that their doctor wasn't actually in network or their plan wasn't what they expected, had no recourse until the following October. MA OEP gives them a second chance to fix it.

If you enrolled in a Medicare Advantage plan in November and by January you realize you made the wrong call—maybe the coverage isn't what you expected, maybe your employer retiree plan interacts badly with it—January through March is your window to fix it.

### The Medigap Timing Issue When Leaving MA

If you use MA OEP to return to Original Medicare, you'll need a Part D plan. That part is straightforward. The tricky part is Medigap.

In most states, if you drop MA and return to Original Medicare outside of a guaranteed issue period, insurers can charge you more or deny your Medigap application based on health. The guaranteed issue rights that applied when you first enrolled at 65 don't automatically apply now.

Exceptions exist—some states have their own rules, and certain qualifying events create guaranteed issue rights. But in the majority of states, if you've been on MA for a few years and developed health conditions, getting back to a comprehensive Medigap policy may cost significantly more than it would have at 65. This is the calculus to think through before going MA in the first place.

Special Enrollment Periods (SEPs) allow you to make changes outside the standard windows when qualifying life events occur. They're crucial safety nets, but they have strict time limits.

### Losing Employer Coverage

If you or your spouse retires or otherwise loses employer-sponsored health insurance, you get an 8-month SEP to enroll in Part B without penalty. The SEP starts the month after employment ends or the month after the employer coverage ends, whichever comes first.

Important: COBRA doesn't count. If your employer coverage ends and you go on COBRA, the SEP starts when employment ends—not when COBRA ends. Don't wait for COBRA to run out before signing up for Medicare. You could end up with a gap and a late penalty.

### Moving Out of Your Plan's Service Area

If you permanently move somewhere your Medicare Advantage or Part D plan doesn't serve, you get a 2-month SEP to join a new plan. Start looking at new options as soon as you know you're moving.

### Plan Losing Its Medicare Contract

If your Medicare Advantage plan decides to stop offering coverage in your area, you get a 2-month SEP to switch. The plan is required to notify you by October 31st of the prior year if it's leaving your area for the following year.

### Five-Star Special Enrollment Period

This one's obscure but real. If a Medicare Advantage or Part D plan has a 5-star rating from CMS (based on quality and member satisfaction), you can switch to that plan at any time during the year—even outside AEP. This SEP can only be used once per year. Most areas don't have 5-star plans but it's worth checking.

### Losing Medicaid or Extra Help

If you lose Medicaid eligibility or lose your Low Income Subsidy (Extra Help) for Part D, you get a 2-month SEP to make coverage changes. You also get an SEP if you newly qualify for Extra Help—you can switch to a plan better suited to your needs.

### Qualifying Events Don't Extend Indefinitely

Most SEPs are time-limited—usually 2 months from the qualifying event. Missing the SEP window means waiting for the next AEP. Document your qualifying events with dates. If you're applying for an SEP and CMS questions it, you'll need to prove when the event occurred.

The General Enrollment Period runs January 1 through March 31 every year. This is for people who missed their Initial Enrollment Period and didn't have a Special Enrollment Period.

You can enroll in Part A and/or Part B during GEP, with coverage starting July 1 of the same year. Notice that gap—if you enroll in January, you don't have coverage until July. Six months with nothing.

You'll pay the late enrollment penalty if applicable.

The GEP isn't where you want to be. If you find yourself considering GEP, make sure you actually don't qualify for an SEP first—call 1-800-MEDICARE and explain your situation before assuming you have no other options.

### Part B GEP and OEP Interaction

If you enroll in Part B during the GEP (January–March), you can also use the ICEP (Initial Coverage Election Period) for Medicare Advantage—the window to enroll in an MA plan when you first get Part B. This used to be complicated, but recent changes mean that if you enroll in Part B through GEP, you have a separate window to then enroll in MA.

It's a sequence, not a simultaneous choice.

As important as knowing what you can do is knowing what you can't—because making moves you don't understand can leave you worse off.

| Enrollment Period | Can Change | Cannot Change | |---|---|---| | AEP (Oct 15–Dec 7) | MA plans, Part D plans, Original Medicare/MA switch | Medigap plans (different rules) | | MA OEP (Jan 1–Mar 31) | Switch MA plans, return to Original Medicare | Join MA for first time, change standalone Part D without leaving MA | | IEP (7 months around 65th birthday) | Parts A, B, C, D all eligible | Must wait for AEP if you miss IEP for MA/Part D | | GEP (Jan 1–Mar 31) | Parts A and B only | MA, Part D (need separate enrollment period) | | SEP (qualifying event) | Depends on qualifying event | Anything not related to the qualifying event |

### Medigap: The Outlier

Medigap (Medicare Supplement) operates on completely different rules than MA and Part D. The guaranteed open enrollment for Medigap is the 6-month period starting the month you're both age 65 and enrolled in Part B. During those 6 months, any insurer offering Medigap in your state must sell you any plan at the standard rate regardless of health status.

Outside that 6-month window, Medigap is medically underwritten in most states (except MA, CT, NY, ME, WA, and a handful of others with continuous open enrollment laws). You can be denied or charged more. AEP does not create Medigap open enrollment.

Theory is one thing. Here's the actual sequence for someone turning 65 with no special circumstances.

### Six to Three Months Before Your 65th Birthday

1. Inventory your current coverage. If you have employer insurance, find out whether it's primary or secondary to Medicare and when it ends. 2. Request a Notice of Creditable Coverage from your employer's benefits administrator for both medical and drug coverage. 3. Start researching Medicare options. Use Medicare.gov's plan finder. Get quotes from Medigap insurers (your premiums will be lowest right at 65). 4. If you're already on Social Security, confirm your automatic Medicare enrollment is proceeding—you should receive your red, white, and blue Medicare card.

### Three Months Before to Birthday Month

5. Enroll in Part A and Part B if not auto-enrolled (SSA.gov is the fastest way). Enroll early in the IEP for earliest coverage start. 6. Decide: Original Medicare + Medigap + Part D, or Medicare Advantage? 7. If going Medigap route: Apply for Medigap during your guaranteed issue period. Compare at least 3–5 insurers for the same plan letter—prices vary significantly for identical coverage. 8. Enroll in a Part D plan (standalone if Original Medicare, or bundled if MA). Compare plans at Medicare.gov using your actual drug list.

### By Your Birthday Month

9. Confirm your enrollment is complete. You should have a Medicare card, your Medigap ID card (if applicable), and your Part D/MA ID card. 10. Verify your doctors and pharmacy are in network (for MA) or accept Medicare (for Original Medicare). 11. Set up premium payment—Part B is typically deducted from Social Security; Part D and Medigap are billed separately unless you set up auto-pay.

### Every Fall Thereafter

12. Read your ANOC (Annual Notice of Change) when it arrives—usually late September. 13. During October, compare your current plan against alternatives on Medicare.gov. 14. Make any changes before December 7. Do it by November 30 if you want to avoid the last-minute rush.