Direct answer: Medicare enrollment windows and penalties run on a calendar. If you miss your first sign-up window and have no qualifying job coverage, the Part B and Part D penalties are added to your monthly premium. They usually last as long as you have that coverage. You sign up for Part A and Part B through Social Security, and it is safest to file early in your 7-month window.
Most people think a missed deadline means a one-time late fee. With Medicare, a missed deadline raises your bill every month, often for the rest of your life. You may also go months with no coverage while you wait for the next window to open.
That is the real trade-off with Medicare enrollment windows and penalties. You can change plans most years. The date you first signed up for Part B usually stays fixed.
If you are reading this at the kitchen table, worried about a parent’s 65th birthday, take a breath. The rules are strict, but you can learn them. A few calls made early will prevent most mistakes.
In my 18 years in insurance marketing, I have watched ads treat Medicare like a holiday sale. The government treats it as a set of named windows with fixed dates and a short list of exceptions.
What are the Medicare enrollment windows?
Medicare has five main windows, and each one does a different job. Ads tend to blur them together.
Two different offices handle these windows. Social Security takes your Part A and Part B sign-up. Private plans and Medicare.gov handle Medicare Advantage and drug plans.
Swipe sideways to see every column.
| Window | Dates | Who it is for | What you can do |
|---|---|---|---|
| Initial Enrollment Period (IEP) | 3 months before your 65th birthday month to 3 months after | People new to Medicare | Sign up for Part A and Part B, then pick a drug or Advantage plan |
| General Enrollment Period (GEP) | January 1 to March 31 | People who missed IEP with no special window | Sign up for Part B, or buy Part A |
| Special Enrollment Period (SEP) | Depends on the event | People who lost job coverage, moved, and similar cases | Sign up or switch, based on the event |
| Open Enrollment | October 15 to December 7 | Anyone with Medicare | Switch plans for January 1 |
| Medicare Advantage Open Enrollment | January 1 to March 31 | People already in an Advantage plan | Make one plan change |
Medigap, the supplement that works with Original Medicare, has its own 6-month clock. We cover it below.
Why does Medicare charge late penalties?
Insurance only works when healthy people pay in along with sick people. If everyone waited until they got sick to join, costs would climb for everyone. The penalty is there to push people to join when they first qualify.
The trap is that many people never get a reminder. You are signed up for Part A and Part B on your own only if you already get Social Security or Railroad Retirement benefits before 65. Everyone else has to apply, and no card shows up in the mail to prompt you.
Full retirement age for Social Security is now past 65. So fewer people are signed up on their own than most folks think. Waiting for a card that never comes is one of the costliest mistakes in Medicare.
What Medicare.gov says the penalties cost in 2026
Medicare.gov’s penalty page lays out how each penalty works. Here is the math with 2026 figures from Medicare.gov’s cost page.
Part B. The penalty is 10% for each full 12-month period you could have had Part B but did not sign up. The 2026 standard premium is $202.90 a month.
Worked example: you wait 2 full years with no special window. That is a 20% penalty. 20% of $202.90 is $40.58. Your new premium is $243.48, rounded to $243.50 a month. You pay that for as long as you have Part B, and it goes up when the standard premium goes up.
Part D. The penalty is 1% of the national base premium for each month you went without drug coverage that counts. Medicare calls that kind of coverage creditable. The 2026 base premium is $38.99.
Worked example: you go 14 months without creditable coverage. 14% of $38.99 is $5.46, rounded to $5.50. That gets added to your plan premium each month. The base premium is reset every year, so the dollar amount can change.
Part A. Most people pay $0 for Part A because they worked about 10 years. If you have to buy it, the 2026 premium is $311 or $565 a month, based on your work history. Sign up late and you pay 10% more, for twice the number of years you waited. If you could have signed up 2 years earlier, you pay the higher amount for 4 years.
Swipe sideways to see every column.
| Part | How the penalty works | 2026 example | How long it lasts |
|---|---|---|---|
| Part B | 10% per full year late | 2 years late: $243.50 instead of $202.90 | Usually as long as you have Part B |
| Part D | 1% of $38.99 per month late | 14 months late: about $5.50 added | Usually as long as you have Part D |
| Part A (bought) | 10% higher premium | 2 years late | 4 years |
There are ways out. You generally will not pay a Part B penalty if you qualify for a special window or join a Medicare Savings Program. You generally will not pay a Part D penalty if you had creditable coverage or get Extra Help. See our guide to Extra Help and Medicare Savings Programs and our page on the Part D late enrollment penalty.
The fine print: job coverage, COBRA and paperwork
The most common special window is for people still working at 65. Per Medicare.gov’s working past 65 page, you may delay Part B if you have group health coverage from current work. That can be your job or your spouse’s job.
You can then sign up any time while you still have that coverage. You also get 8 months after the job ends or the coverage ends, whichever comes first. Coverage usually starts the first of the month after you sign up.
Employer size matters. With 20 or more employees, the job plan usually pays first, so waiting on Part B is often safe. With fewer workers, Medicare usually pays first, and skipping Part B can leave big gaps.
COBRA does not stop the clock
COBRA feels like job coverage, but Medicare does not count it that way. Your 8-month clock starts when you stop working, even if you choose COBRA. Suppose you keep COBRA for a year and think Part B can wait. Your 8 months could run out before you notice.
Retiree coverage does not count as current work either. Neither do Marketplace plans or VA coverage, and none of them opens this window.
The form your employer has to sign
When you sign up through this special window, Social Security needs a form showing you had job-based coverage. Your employer has to fill out part of it. Start it a month or two before you need coverage, and keep copies. Penalty disputes are decided on paper.
If you have a Health Savings Account, you have to stop putting money in once Medicare starts. Part A can reach back up to 6 months. Ask your benefits office about timing before you file. Our guide to Medicare and working past 65 walks through this.
Is the usual advice wrong?
Some common advice sounds fine but costs people money. Here are three examples.
Signing up in your birthday month
Your birthday month feels like the natural time to file. It can leave a gap. Per Medicare.gov’s sign-up page, if you sign up before your birthday month, Part B starts the first day of that month. If you sign up in your birthday month or later, it starts the first of the month after you sign up.
The 3 months before your birthday month are the safer time to file.
Switching later at Open Enrollment
You can switch between Medicare Advantage and Original Medicare most falls. Getting a Medigap policy later is a different story. Your Medigap open window lasts 6 months and starts when you are 65 or older and have Part B. During that window, insurers in most cases have to sell you a policy no matter your health, per Medicare.gov’s Medigap page.
After that window, insurers in most states can check your health and turn you down. State rules vary, so check with your state insurance department. Read more in Medigap open enrollment at 65.
Fixing mistakes from January to March
Two windows share the January 1 to March 31 dates. The General Enrollment Period is for people who still need Part B. The Advantage Open Enrollment Period is only for people already in an Advantage plan.
You cannot use January to March to move from Original Medicare into an Advantage plan. That move happens in the fall, during your first window, or in a special window. If you sign up for Part B during the GEP, coverage starts the first of the month after you sign up. The penalty still applies. Our OEP and AEP checklist lays out each window.
Where the money goes
Signing up for Part A and Part B through Social Security is free. Nobody earns a commission on it.
The money is in the next step. Insurers pay agents and brokers when someone joins an Advantage plan, a drug plan, or a Medigap policy. In lead generation, a person about to turn 65 is one of the most prized names on a list, because one sale can pay out for years.
That is why the mail and calls pile up around a 65th birthday. The flood tells you who wants a commission. It does not tell you your deadline. In my years in this business, I have seen ads lean on fear of a deadline to rush people toward one plan.
Medicare.gov’s Plan Compare tool shows the same plan data that brokers use, priced against your own drugs. Your state’s free SHIP counselors can help, and they are not paid based on what you pick.
Related: compare Medicare Advantage vs Original Medicare, see Medigap vs Medicare Advantage, and check your bill in Part B premiums and IRMAA.
Six moves before your 65th birthday
- Find out if you will be signed up on your own. If you do not get Social Security benefits yet, plan to apply.
- Check your work record. Log in to your Social Security account and confirm about 10 years of work. That is the difference between free Part A and up to $565 a month.
- Ask HR two questions in writing. How many employees does the company have? Is the drug coverage creditable? Keep the answers.
- Decide on Part B. If you are delaying it, get the employer form started early.
- File in the 3 months before your birthday month. Use Social Security’s sign-up page, call, or visit an office. Save your confirmation number.
- Pick your path before the Medigap clock runs out. Decide between Original Medicare with a supplement and an Advantage plan within your 6-month Medigap window.
What not to do
Do not wait for a card that may never come. Do not treat COBRA as job coverage. Do not throw away the yearly creditable coverage notices from your employer. And do not sign up with the first caller who says your deadline is tomorrow.
Frequently asked questions
Do I sign up with Medicare or with Social Security?
You sign up for Part A and Part B with Social Security, online, by phone, or at a local office. Railroad retirees use the Railroad Retirement Board. Medicare runs the program, but Social Security takes the application. You join a Medicare Advantage or Part D plan separately, through the plan itself or through Medicare.gov.
How long does the Part B penalty last?
Usually for as long as you have Part B, which for most people means the rest of their life. It adds 10% for each full 12-month period you could have signed up but did not. In 2026, waiting 2 years turns the $202.90 standard premium into about $243.50 a month, and that amount grows as the standard premium rises.
Does COBRA let me delay Part B?
No. The 8-month special window for job coverage starts when you stop working or lose that job coverage, even if you choose COBRA. COBRA does not count as coverage from current work. If you wait until COBRA ends, you may have missed your window and face both a coverage gap and a Part B penalty.
If I miss my first window, when does coverage start?
Without a special window, you sign up during the General Enrollment Period, January 1 to March 31. Under the current rule, Part B starts the first day of the month after you sign up. If you enroll in February, coverage starts March 1. Some older booklets still say July 1, so trust the live Medicare.gov page.
Is $38.99 the price of a Part D plan in 2026?
No. $38.99 is the national base premium, a number Medicare uses to figure the Part D late penalty and the income-based add-on. Real plan premiums vary by plan and by where you live. To see what plans near you cost with your drugs, use Plan Compare on Medicare.gov or ask your SHIP counselor.
Your next step
Look at your calendar today and find your 65th birthday month. Count back 3 months. That is when to file with Social Security. If you or a parent is still working, ask HR for the employee count and a creditable coverage letter this week.
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