Why Medicare Has So Many Windows

Medicare is not like the group plan you had at work, where everyone signs up on day one and re-picks in the fall. It is a set of separate programs, and each has its own door. Parts A and B come from the federal government. Part D drug plans, Medicare Advantage plans, and Medicare Supplements (Medigap) come from private insurance companies.

One idea sits underneath all of it. Medicare is built to keep you continuously covered, and it charges the people who wait. The late penalties are not fees you pay once. They are added to your premium every month for as long as you have the coverage.

The windows are predictable, though. Seen on one page, the calendar stops being scary. For the bigger picture first, start with how Medicare works.

Every Medicare Enrollment Window at a Glance

Source: medicare.gov, 2026 (full links under Sources)

The Initial Enrollment Period: Your First 7 Months

Your Initial Enrollment Period is the 7-month window built around your 65th birthday: the 3 months before your birthday month, the month itself, and the 3 months after. It is the door most people walk through.

If you already receive Social Security at 65, Parts A and B are generally started for you. If not, nothing happens until you act, and you act through Social Security, not through Medicare and not through us. Our job is making sure you know which month, and what to do the day after.

Timing inside the window matters. Sign up in the 3 months before your birthday month and coverage can begin the first day of that month. Sign up during your birthday month or in the 3 months after, and Part B starts the first day of the month after you sign up. Coverage always starts on the first of a month.

Most people pay no monthly premium for Part A, because they or a spouse paid Medicare taxes for at least 40 quarters, so there is rarely a reason to delay it. Part B carries a premium, which is where the “should I wait” question comes from, and the answer turns on whether you have coverage from a current employer. Our Turning 65 page walks through that first meeting.

Working Past 65: The Special Enrollment Period

If you are still working at 65 with health coverage through your job, or your spouse’s job, Medicare lets you delay Part B without a penalty. That permission has three rules.

The 8-month clock

When your employment or the group coverage ends, whichever comes first, an 8-month Special Enrollment Period opens the following month, and inside it you can enroll in Part B with no penalty. Do not use all 8 months: your Part B start date is what opens your Medigap window and lets a Part D or Advantage plan begin. Our Leaving Employer Coverage page covers the hand-off.

The 20-employee rule

With 20 or more employees, the group plan pays first and Medicare second, so you may delay Part B. With fewer than 20, Medicare pays first, and without Part B the group plan may pay very little. Ask HR which side of the line you are on.

COBRA and retiree coverage do not count

This is the rule that catches careful people. COBRA and retiree plans are not coverage based on current employment. They do not let you delay Part B without a penalty, and losing them does not open a Special Enrollment Period. Your 8 months started when the job ended, whether or not COBRA was running.

A composite from our offices. A man in the Valley retired in late summer, and his company kept him on the group plan at employee rates for several more months. He had turned 65 about two years earlier and planned to deal with Medicare the following year. Then his wife read the paperwork closely. The continuation was COBRA. She called our office rattled: his 8-month clock had started the month after his last day at work, not the month COBRA would end. Because she called that fall, he was still inside the window and enrolled with no penalty. Had they waited until the following year as planned, the only door left would have been the General Enrollment Period, with a penalty for life.

The General Enrollment Period: The Repair Window

If your Initial Enrollment Period passed without Part B and you have no Special Enrollment Period, there is one door left: the General Enrollment Period, January 1 to March 31 every year. You sign up, and coverage starts the month after you do.

That is the whole window, and it does not erase the time you waited. The Part B late enrollment penalty is 10% of the standard Part B premium for each full 12-month period you could have had Part B and did not, for life. In 2026 the standard premium is $202.90, so each full 12-month period of waiting adds 10% of $202.90, or $20.29 a month, every month, rising as the premium rises.

A composite from our offices. A woman in her late 60s came to us already on Medicare. Years earlier she had let her Initial Enrollment Period go by without Part B. She had no employer plan, had not needed a doctor, and did not want another bill. When she finally enrolled, the penalty was set, and it has been added to her Part B premium every month since. One year the Social Security deduction stopped working, the bill arrived from her plan instead, and she spent months on the phone over a charge she never wanted. Her husband enrolled on time; his premium has no such line. Nothing we, or anyone, can do removes hers. The lesson is not carelessness. It is that the penalty is permanent, and the only way to avoid it is to know the window before it closes.

The Annual Enrollment Period: October 15 to December 7

Once you are on Medicare, the Annual Enrollment Period is your yearly chance to change the private side of your coverage. From October 15 to December 7 you can join, switch, or drop a Medicare Advantage plan, and join, switch, or drop a Part D drug plan. Whatever you choose takes effect January 1 of the next year, as long as the plan gets your request by December 7.

Three things people get wrong about it:

• It is not about Part B. Nothing here enrolls you in Part B or forgives a penalty. Part B goes through Social Security in the windows above.
• It is not a Medigap window. Outside your own 6-month open enrollment there is no federal guarantee a company will sell you a Medigap policy; the company can use medical underwriting and decline you unless a guaranteed issue right applies, and some states add rights under state law.
• Doing nothing is a decision. Plans change their doctor networks, drug lists, and costs every year. If your plan changed and you did not look, you chose the new version of it.

Not sure last year’s plan still fits? Start with Already on Medicare. Every fall we review each client’s doctors and prescriptions against the coming year’s plans, which is the reason the window exists.

The Medicare Advantage Open Enrollment Period: The January Do-Over

For many people the first real test of a new plan comes in January, at the pharmacy counter or a doctor’s front desk. Medicare built a second chance for exactly that. If you are in a Medicare Advantage plan on January 1, you get one change during the Medicare Advantage Open Enrollment Period, January 1 to March 31: switch to a different Advantage plan, or leave Advantage and return to Original Medicare with a Part D plan.

It does not let someone on Original Medicare join an Advantage plan, and whether a Medigap policy will take you back depends on a guaranteed issue right, covered next.

A composite from our offices. A woman in the Valley moved from her Medicare Supplement to an Advantage plan for the new year. In the first weeks of January her doctor’s front desk told her the primary care doctor she had seen for a decade was not in the new plan’s network. We pulled the plan’s directory with her on the phone. Her doctor was in it, but the scare made her look harder at the plan, and she did not like what she saw. Because it was still January, she had a clean choice: a different Advantage plan whose network held every doctor on her list, or back to Original Medicare, with a Supplement if a guaranteed issue right applied. She changed plans in February. A man who made the same move and first called us in midsummer had no such choice: his window had closed, leaving the next Annual Enrollment Period and an underwritten Supplement application.

Medigap Open Enrollment and Guaranteed Issue

A Medicare Supplement (Medigap) is the one piece of Medicare where your health can be held against you, which is why its window matters. Your Medigap open enrollment period is a 6-month, one-time window that starts the first month you are both 65 or older and enrolled in Part B. During those 6 months an insurance company must sell you any Medigap policy it offers in your state, with no health questions.

Notice the trigger. It is Part B, not your birthday. If you delay Part B for work, your Medigap window opens the month Part B begins. That is good news for people who plan, and a trap for people who take Part B “just in case” at 65 while still working and let the 6 months run out unused.

After the window closes, there is no federal guarantee that a company will sell you a Medigap policy. The company can use medical underwriting: ask about your health, charge more, or decline you. Some states offer more chances to buy under state law; your State Insurance Department can tell you what applies where you live. The exception is a guaranteed issue right: a situation, usually outside your control, where the law says a company must take you. Examples include an employer plan that ends, an Advantage plan that leaves your area or leaves Medicare, and a trial right if you joined a Medicare Advantage plan for the first time and return to Original Medicare within 12 months of joining. Each comes with a deadline: apply no more than 63 days after the coverage ends (you can apply up to 60 days before it ends), and each has to be proven on paper. Keep every letter about coverage ending; we have watched an application sit for weeks because one went to an old address.

The Part B and Part D Late Penalties

Both penalties share three traits: they grow with how long you waited, they are added to your premium every month, and they never go away.

The Part B penalty

10% of the standard Part B premium for each full 12-month period you could have had Part B and did not, for as long as you have Part B. Months covered by a current employer’s plan do not count against you. Months on COBRA, retiree coverage, or nothing at all do.

The Part D penalty

1% of the national base beneficiary premium for each full month you went without Part D or other creditable drug coverage, rounded to the nearest 10 cents, for as long as you have Part D. The 2026 base premium is $38.99, so 24 uncovered months would add 24% of $38.99, which is $9.36, rounded to $9.40 a month. The penalty applies if, at any time after your Initial Enrollment Period ends, you go 63 or more days in a row without Medicare drug coverage or other creditable drug coverage, and because the penalty is tied to the national base premium, it follows you to every plan you ever join.

A composite from our offices. A man in his 70s kept drug coverage through a former employer for years after retiring. When it ended, he did nothing; he took no regular medications and saw no reason to pay for a drug plan. More than a year later a new prescription changed his mind, and he called to ask how much the penalty would be and whether there was a way around it. We did the math with him on the phone. It was a small number, it was permanent, and there was no way around it, because he had genuinely been uncovered. He joined a plan that week. Creditable drug coverage is not about today’s pills. It is about the penalty clock.

What to Do This Fall

The Annual Enrollment Period runs October 15 to December 7. Here is the order we use in our offices.

1. Find your window first. Turning 65 this year: Turning 65. Retiring or losing group coverage: Leaving Employer Coverage. Already enrolled: Already on Medicare.
2. Learn the moving parts early. Our Medicare Made 123Easy workshop is Friday, October 2, 2026, before the Annual Enrollment Period opens, on purpose. Save your seat for Friday, October 2, 2026.
3. List your doctors and prescriptions. Networks and drug lists change every year.
4. Sit down with a Certified Medicare Planner®. We pull up every plan available in your ZIP code, load your doctors and medications, and shop together on screen. Talk to an advisor.

If you missed a window this year, do not wait for a better one. Call. The penalty math only gets worse with time, and there are more Special Enrollment Periods than people think.