Medicare has six fixed enrollment periods, and each one controls a different kind of change you can make to your coverage. Some are tied to your 65th birthday, some run on the calendar every year, and some open only when a specific life event triggers them. Getting the timing right matters: missing the window that applies to you can mean permanent premium surcharges or months without coverage while you wait for the next opening.
Here is how each window works, who it applies to, and what you can do inside it.
Initial Enrollment Period
Your first opportunity to sign up for Medicare is a seven-month window built around your 65th birthday. It begins three months before the month you turn 65, includes your birthday month, and continues for three months after.1Medicare.gov. When Does Medicare Coverage Start For most people, this is the single most important Medicare deadline they will face.
When your coverage actually starts depends on when in the window you enroll. Sign up in any of the three months before your birthday month and coverage begins the month you turn 65. Wait until your birthday month or later, and coverage starts the following month.1Medicare.gov. When Does Medicare Coverage Start The practical takeaway is to enroll early in the window so coverage is in place when you need it. One quirk: if your birthday falls on the first of the month, coverage starts the month before you turn 65.
Most people qualify for premium-free Part A because they or a spouse paid Medicare taxes for at least 10 years. The standard Part B premium is $202.90 per month in 2026.2Centers for Medicare & Medicaid Services. 2026 Medicare Parts A and B Premiums and Deductibles
General Enrollment Period
The General Enrollment Period runs from January 1 through March 31 each year. It exists for people who missed their Initial Enrollment Period for Part B or for premium Part A and do not qualify for a Special Enrollment Period.3Centers for Medicare & Medicaid Services. Original Medicare (Part A and B) Eligibility and Enrollment Coverage starts the month after you sign up.1Medicare.gov. When Does Medicare Coverage Start
Think of this as a safety net rather than a normal option. Signing up here almost always means late enrollment penalties, and the gap between your 65th birthday and the next January can leave you without coverage for months.
Annual Enrollment Period
From October 15 through December 7 every year, anyone with Medicare can make changes to their coverage for the following year.4Medicare. Open Enrollment This is often called Open Enrollment. Any change takes effect January 1.
During this window you can:
- Switch from Original Medicare to a Medicare Advantage plan, or the other way around
- Change from one Medicare Advantage plan to another, with or without drug coverage
- Join, switch, or drop a Part D prescription drug plan if you are in Original Medicare
Plans update their costs, provider networks, and drug formularies each year. A medication that was affordable last year might move to a higher cost tier, or a cheaper plan might now cover your local providers. Even if you are content with your current plan, this window is worth using to check. Changes have to reach your plan by December 7 to take effect January 1.5Medicare.gov. Joining a Plan
Medicare Advantage Open Enrollment Period
If you are already in a Medicare Advantage plan, you get a separate window from January 1 through March 31 to make one additional change.6Medicare.gov. Understanding Medicare Advantage and Medicare Drug Plan Enrollment Periods Only one change is allowed in this window, so use it carefully.
Your two options are:
- Switch to a different Medicare Advantage plan
- Drop Medicare Advantage and return to Original Medicare, with the option to add a Part D drug plan
Whatever change you make takes effect the first day of the month after your plan receives the request. Switch in February and the new coverage begins March 1. This period does not apply to people in Original Medicare; it is only for current Medicare Advantage enrollees who want to adjust after Annual Enrollment has closed.
Special Enrollment Periods
Special Enrollment Periods let you sign up or change plans outside the regular calendar windows when specific life events happen. For anyone still working past 65, this is arguably the most important enrollment opportunity, and it is also the one people most often misunderstand.
Still Working at 65
If you or your spouse are still working and you are covered under an employer group health plan, you can delay Part B without penalty. Once the employment ends or the group coverage stops, whichever comes first, you have an eight-month Special Enrollment Period to sign up for Part B and premium Part A.3Centers for Medicare & Medicaid Services. Original Medicare (Part A and B) Eligibility and Enrollment You can also enroll at any point while you are still covered under the employer plan.
This is where expensive mistakes happen. COBRA coverage and retiree health plans do not count as coverage based on current employment, so they do not trigger a Special Enrollment Period. If you leave your job, go on COBRA, and plan to sign up for Part B when COBRA runs out, you will miss the eight-month window and end up waiting for the next General Enrollment Period, with a penalty attached.
Other Qualifying Events
Several other life changes open a Special Enrollment Period:7Medicare. Special Enrollment Periods
- Moving out of your plan’s service area: two full months after the move to switch plans or return to Original Medicare
- Losing Medicaid eligibility: three months to join a Medicare Advantage or Part D plan
- Losing other creditable drug coverage involuntarily: two months after the loss to join a drug plan
- Moving back to the U.S. after living abroad: two months to join a plan
- Being released from incarceration: two months to join a plan, provided you kept Part A and/or Part B while incarcerated
- Living in or leaving an institution such as a nursing home: you can make changes the entire time you live there and for two months after moving out
Medicare also recognizes exceptional circumstances case by case, such as being misled by a plan representative or facing a major change to your plan’s provider network.7Medicare. Special Enrollment Periods
Medigap Open Enrollment Period
Medigap, also called Medicare Supplement Insurance, has its own one-time enrollment window that runs on different rules from the rest of Medicare. It begins the first month you have Part B and are 65 or older, and it lasts six months.8Medicare. Get Ready to Buy During this window, no insurance company can deny you a Medigap policy or charge you more because of pre-existing health conditions.
Once the six months are up, insurers in most states can use medical underwriting to decide whether to sell you a policy and what to charge for it. A health condition that would not have mattered inside the window can price you out of Medigap entirely once the window closes. If you think you might ever want a Medigap plan, this is the time to act. Some states offer additional protections beyond the federal minimum, but the six-month federal window is the baseline everywhere.
What Missing an Enrollment Period Costs
Missing the right window does more than delay coverage. For Part B and Part D, it triggers permanent premium surcharges that follow you for life.
Part B Penalty
The Part B late enrollment penalty adds 10% to your standard monthly premium for every full 12-month period you were eligible but did not enroll. Three years of delay means a 30% surcharge on the base premium, and for most people that surcharge lasts as long as they have Part B.9Medicare. Avoid Late Enrollment Penalties The penalty does not apply if you qualify for a Special Enrollment Period, such as the one for employer coverage.
Part D Penalty
A Part D penalty kicks in if you go 63 or more consecutive days without Medicare drug coverage or other creditable prescription drug coverage after your Initial Enrollment Period. The penalty equals 1% of the national base beneficiary premium, which is $38.99 in 2026, multiplied by the number of full months you went without coverage.10Centers for Medicare & Medicaid Services. 2026 Medicare Part D Bid Information and Part D Premium Stabilization Demonstration Parameters Twenty months without creditable coverage produces a penalty of about $7.80 per month, added to your Part D premium permanently.
Part A Penalty
Most people get Part A premium-free and face no penalty. If you do have to pay a Part A premium and enroll late, the penalty is 10% of the monthly premium, and it lasts twice as long as you delayed. Delay by two years and you pay the surcharge for four. Unlike the Part B and Part D penalties, this one eventually expires.
If You Qualify for Medicare Before 65
Most of these enrollment windows are built around turning 65, but Medicare also covers some people earlier. If you receive Social Security Disability Insurance benefits, Medicare starts automatically after 24 months of those benefits.11Medicare.gov. Which Path Is Right for Me People with ALS or end-stage renal disease qualify on different timelines. The enrollment periods work the same way, but the clock is set to your Medicare eligibility date instead of your 65th birthday.
Enrollment Period Quick Reference
- Initial Enrollment Period. Seven months around your 65th birthday (three months before, the birthday month, three months after). Sign up for Part A and Part B.
- General Enrollment Period. January 1 through March 31. Safety net for people who missed their Initial Enrollment Period. Late penalties likely apply.
- Annual Enrollment Period. October 15 through December 7. Switch plans or change coverage for the following year.
- Medicare Advantage Open Enrollment Period. January 1 through March 31. One plan change for current Medicare Advantage enrollees only.
- Special Enrollment Periods. Triggered by specific life events like losing employer coverage or moving. Duration varies by event.
- Medigap Open Enrollment. Six months starting when you first have Part B and are 65 or older. One-time window for guaranteed access to Medigap policies.