Medicare enrollment does not run on one single date for everyone. Depending on your situation, you might have a seven-month window around your 65th birthday, a yearly fall review, a narrow spring window if you already have an Advantage plan, or a special window triggered by a life event. Mixing up these dates can mean months of waiting for coverage to start, or a penalty that follows you for as long as you have Medicare. This guide walks through the four main enrollment periods for 2026, the penalties tied to being late, and a short checklist to get ready.
Initial Enrollment Period (IEP)
Your Initial Enrollment Period is the seven-month window built around your 65th birthday: it starts three months before the month you turn 65, includes your birthday month, and continues three months after. If you enroll during the three months before your birthday month, coverage generally starts the first day of that month. Enroll later in the window and your start date moves back, in some cases by several months.
Because this window opens once and does not repeat, it is worth marking your calendar as soon as you know your 65th birthday is on the horizon, even if you feel healthy and are still deciding whether you need Part B right away, for example because you are still working and have employer coverage.
Annual Enrollment Period (AEP): October 15 – December 7
Every fall, from October 15 through December 7, the Annual Enrollment Period lets anyone with Medicare review their coverage for the following year. During AEP you can switch from Original Medicare to a Medicare Advantage plan, move back to Original Medicare, change from one Advantage plan to another, or join, drop, or switch a Part D prescription drug plan. Any change made during AEP takes effect January 1.
Plans commonly adjust their premiums, networks, and drug formularies each year, so even people who are happy with their current plan benefit from a short annual check to confirm their doctors and medications are still covered the way they expect.
Medicare Advantage Open Enrollment Period (OEP): January 1 – March 31
The Medicare Advantage Open Enrollment Period runs January 1 through March 31 and is only available to people who are already enrolled in a Medicare Advantage plan on January 1. During this window you can make one change: switch to a different Medicare Advantage plan, or drop Advantage entirely and return to Original Medicare (adding a standalone Part D plan if needed).
Unlike AEP, OEP does not let you switch from Original Medicare into an Advantage plan, and you only get to use it once per year. It exists mainly as a safety valve for people who realize in January or February that their new plan year is not working the way they expected.
Special Enrollment Periods (SEP)
Outside of the three scheduled windows above, certain qualifying life events can open a Special Enrollment Period. Common triggers include moving outside your plan's service area, moving to an area with new plan options, losing employer or union coverage, losing Medi-Cal, or moving into or out of a skilled nursing facility.
Each qualifying event carries its own timeline and rules — some give you two months, others longer — so if something in your coverage or living situation has changed recently, it is worth checking whether a SEP applies to you rather than assuming you must wait for AEP.
Late enrollment penalties for Part B and Part D
Timing is not only about convenience. If you do not sign up for Part B when you are first eligible and do not have qualifying employer coverage, Medicare can add roughly 10 percent to your Part B premium for each full 12-month period you were eligible but not enrolled — and that penalty applies for as long as you have Part B.
Part D works similarly: if you go 63 or more days in a row without creditable drug coverage after your Initial Enrollment Period ends, a separate late enrollment penalty is added to your Part D premium, and it also generally lasts for as long as you carry that coverage. Reviewing your enrollment dates ahead of time is one of the simplest ways to avoid a charge that follows you indefinitely.
Availability, cost, benefits, and eligibility vary by person, product, contract, and insurance company, as well as by your service area. Guarantees are subject to the claims-paying ability of the issuing insurance company. Karla Arámburo is not affiliated with or endorsed by Medicare or the federal government.
A short checklist before any enrollment window
Before AEP, OEP, or your own Initial Enrollment Period opens, it helps to have the following ready:
- A current list of your doctors and specialists
- A complete list of your prescriptions, including dosages
- The pharmacies you actually use
- A rough monthly budget for premiums, copays, and expected care
- Any planned travel that could affect where you need network access
Having these on hand turns a plan comparison into a short, specific conversation instead of a guessing game.
If your income is limited
If your income and resources are limited, you may qualify for Extra Help with Part D drug costs, or for a Medi-Medi (Medicare and Medi-Cal) status that can lower or eliminate many out-of-pocket costs. These programs have their own eligibility rules and application windows, separate from the enrollment periods described above. You can read more about these income-based programs on our frequently asked questions page.
A bilingual, local resource in Southern California
Karla Arámburo is a bilingual, licensed insurance agent serving Southern California, and reviewing your enrollment timeline with her costs nothing and comes with no pressure to enroll. Beyond Medicare, she also works with life insurance options that accept an ITIN for families that do not have a Social Security number. You can call or text (619) 321-8733, explore our Medicare services, compare our guide on Medicare Advantage vs. Original Medicare, or see how these dates apply if you live in El Cajon. This page is general education, not individualized advice or an enrollment recommendation.
Frequently asked questions
What happens if I miss my Initial Enrollment Period?
If you do not have active employer coverage that counts as creditable and you let your IEP pass without enrolling in Part B, you will typically have to wait for the General Enrollment Period (January 1 through March 31, with coverage starting later) and you may face a permanent late enrollment penalty. Confirming your exact eligibility date ahead of time avoids that coverage gap.
Can I switch Medicare plans at any point during the year?
No. Outside of your IEP, changes are only possible during AEP (October 15 through December 7), OEP if you already have an Advantage plan (January 1 through March 31), or if you qualify for a Special Enrollment Period triggered by an event such as a move or losing employer coverage.
During OEP, can I add drug coverage if I don't already have it?
OEP is only available to people who are already enrolled in a Medicare Advantage plan on January 1. You can use it to switch to a different Advantage plan (with or without drug coverage) or to return to Original Medicare and add a standalone Part D plan, but you cannot use OEP to move from Original Medicare into an Advantage plan for the first time.
What counts as a qualifying event for a Special Enrollment Period?
The most common triggers include moving outside your plan's service area, moving to an area with new plan options, losing employer or union coverage, losing Medi-Cal, or moving into or out of a skilled nursing facility. Each event has its own timeline, so it is worth confirming your specific situation rather than assuming one general rule applies.
How much exactly is the Part B late enrollment penalty?
Generally, Medicare can add roughly 10% to your monthly Part B premium for each full 12-month period you were eligible but did not enroll, without creditable employer coverage. That penalty typically applies for as long as you have Part B, not just for one year.
When do changes made during AEP take effect?
Any plan change made during AEP (October 15 through December 7) takes effect on January 1 of the following year, regardless of which day within the window you made the change.
If my income is low, is there help available to pay for my prescriptions?
Yes. The Extra Help program can lower your Part D premiums, deductibles, and copays, and if you also qualify for Medi-Cal (a status known as Medi-Medi), many out-of-pocket costs can drop considerably. These programs have their own income and resource rules, separate from Medicare's enrollment periods.