The Medicare Part B late enrollment penalty is an extra amount added to your monthly Part B premium if you waited too long to sign up and did not have qualifying coverage.
The basic rule is simple: 10% is added to the standard Part B premium for each full 12-month period you could have had Part B but did not enroll. In most cases, you pay that penalty for as long as you have Part B.
That is why this mistake matters. A short delay may not create a penalty. A delay of several full years can follow you every month for the rest of your Medicare life.
How the Part B Late Enrollment Penalty Works
Medicare calculates the Part B penalty in full 12-month periods.
If you delayed Part B for:
- less than 12 full months, you may not owe a Part B penalty
- 12 full months, the penalty is usually 10%
- 24 full months, the penalty is usually 20%
- 36 full months, the penalty is usually 30%
The percentage is applied to the standard Part B premium, not necessarily to what you personally pay after IRMAA or other adjustments.
For example, Medicare’s standard Part B premium in 2026 is $202.90 per month. A 20% penalty would add about $40.58 per month, bringing the Part B amount to about $243.48 per month before any other adjustments.
That extra amount is not a one-time fee. It is usually added to your Part B premium every month.
When Does the Penalty Usually Apply?
The penalty usually becomes a risk when both of these are true:
- you did not sign up for Part B when you were first eligible
- you did not have a valid Special Enrollment Period based on qualifying coverage
For many people, the first chance to sign up for Medicare is the 7-month Initial Enrollment Period around the 65th birthday. If you miss that window and do not have qualifying employer coverage, the penalty clock can start.
If you are just starting the Medicare timeline, this broader checklist may help: What Do You Need to Do Before Turning 65? Medicare Checklist.
What Coverage Lets You Delay Part B Without a Penalty?
The cleanest protection is usually group health coverage based on current active employment.
That can mean coverage from:
- your own current job
- your spouse’s current job
If you are still working at 65 and covered by an employer plan, the employer size matters. In general, if the employer has 20 or more employees, that employer coverage can allow you to delay Part B without a late enrollment penalty.
If the employer has fewer than 20 employees, Medicare usually becomes primary at 65. In that situation, delaying Part B can create both a penalty problem and a claims problem.
I break out that working-past-65 rule here: Do You Need Medicare at 65 If You’re Still Working? Missouri Rules.
The 8-Month Special Enrollment Period
If you delay Part B because you have qualifying active employer coverage, you usually get an 8-month Special Enrollment Period when that employment or coverage ends.
The key detail is that the clock starts when the active employment ends or the active employer coverage ends, whichever happens first.
Do not wait for COBRA to run out. Do not wait for retiree coverage to end. Those are different situations, and they do not extend the Part B Special Enrollment Period the same way active employer coverage does.
If you already retired and need the practical steps, read How to Apply for Medicare Part B After Employer Coverage Ends.
Coverage That Often Does Not Protect You
This is where people get burned. They hear “I still have insurance” and assume that means Medicare can wait.
That is not always true.
Coverage that often does not protect your Part B timing includes:
- COBRA
- retiree health coverage
- Marketplace coverage
- individual health insurance that is not based on current active employment
Those plans may still pay claims in some situations. That does not automatically mean they protect you from the Part B late enrollment penalty.
If COBRA is involved, slow down and read this before making a decision: Medicare and COBRA: The Expensive Mistake Thousands of Retirees Make.
If retiree insurance is involved, start here: Can You Delay Medicare Part B If You Have Retiree Insurance?.
Part B and Part D Penalties Are Not the Same
Part B and Part D both have late enrollment penalties, but they are calculated differently.
For Part B, the penalty is generally 10% for each full 12-month period you delayed without qualifying coverage.
For Part D, the penalty is based on the number of months you went without creditable prescription drug coverage after your Medicare drug coverage window started.
That is why the phrase “creditable coverage” can be misleading. Coverage that helps with Part D may not protect your Part B timing. Coverage that protects Part B may still need to be checked separately for drug coverage.
For the broader explanation, read What Is Creditable Coverage for Medicare?.
Can You Get the Part B Penalty Removed?
Sometimes people ask whether the penalty can be appealed.
The honest answer: it depends, and you should not assume it will be removed just because the mistake was understandable.
If Social Security believes you missed your valid enrollment window, the penalty can be very hard to undo. The strongest cases usually involve proof that you actually did have qualifying coverage or that the enrollment record is wrong.
That is why paperwork matters. Keep copies of:
- employer coverage dates
- employment end dates
- CMS-L564 employer verification forms
- Social Security or Medicare enrollment confirmations
- retiree, COBRA, or Marketplace notices that clarify what coverage you had
If you are not sure whether your coverage counted, ask before the window closes. It is much easier to prevent the penalty than to fight it later.
What I Would Check Before Delaying Part B
Before telling anyone in Missouri or the Kansas City area to delay Part B, I would want clear answers to these questions:
- Are you still actively working?
- Is the coverage from your current job or your spouse’s current job?
- Does the employer generally have 20 or more employees?
- Are you on COBRA, retiree coverage, or Marketplace coverage instead?
- Are you contributing to an HSA?
- When exactly will employment or active employer coverage end?
That last question matters more than people think. The Part B Special Enrollment Period is based on dates, not intentions.
If an HSA is part of the picture, read Medicare and HSA Contributions After 65: The Tax Trap Many Missouri Workers Miss before enrolling in any part of Medicare.
The Practical Bottom Line
The Part B late enrollment penalty is not complicated because of the math. It is complicated because people often misunderstand which coverage lets them delay Part B safely.
Active employer coverage from current work may protect you. COBRA, retiree coverage, and Marketplace coverage usually should not be treated the same way.
If you are approaching 65, retiring after 65, or leaving employer coverage, confirm the rule before you wait. A 10%, 20%, or 30% penalty may not sound dramatic at first, but when it is added to your premium every month, it becomes a very expensive paperwork mistake.
Official Sources
For the current rules, start with Medicare’s pages on avoiding late enrollment penalties, when you can sign up for Medicare, and working past 65. Social Security also has a useful page on how to sign up for Part B only.
Frequently Asked Questions
How much is the Medicare Part B late enrollment penalty?
The Part B late enrollment penalty is generally 10% of the standard Part B premium for each full 12-month period you could have had Part B but did not sign up and did not qualify for a Special Enrollment Period.
Do you pay the Part B penalty forever?
In most cases, yes. Medicare says the Part B late enrollment penalty is paid for as long as you have Part B. That is why the timing decision is so important.
Does COBRA let me delay Medicare Part B without a penalty?
Usually no. COBRA is not the same as active employer coverage for Part B timing. If you are 65 or older and leaving work, your 8-month Special Enrollment Period generally starts when active employment or active employer coverage ends, not when COBRA ends.
Does retiree insurance count for Part B?
Usually no. Retiree coverage is normally different from coverage based on current active employment. Many retiree plans expect Medicare to be primary once you are eligible.
What if I missed Part B because I was given bad advice?
Get your documents together and contact Social Security. A penalty is easier to avoid than remove, but if the record is wrong or you had qualifying coverage, documentation matters.