You're about to turn 65, but you're still working. Your employer offers health insurance, you feel great, and retirement isn't even on your radar yet. Then the Medicare letters start arriving, and suddenly you're facing a decision that feels way more complicated than it should be: Do I sign up for Medicare Part B now, or can I wait?
It's a legitimate question: and one that thousands of working seniors wrestle with every single year. The answer isn't the same for everyone, and making the wrong choice could cost you thousands of dollars in penalties down the road.
Let's break this down so you can make the right call for your situation.
Why This Decision Matters
Medicare Part B covers things like doctor visits, outpatient care, preventive services, and medical equipment. It's essential coverage: but it also comes with a monthly premium. In 2026, most people pay around $185 per month for Part B, though higher earners pay more.
If you're still getting solid health insurance through your job, paying for Medicare Part B on top of that might feel like throwing money away. And you know what? In many cases, you'd be right.
The good news is that if you have qualifying employer coverage, you can delay Part B enrollment without facing those dreaded late enrollment penalties. But: and this is a big but: there are specific rules you need to follow.
The Magic Number: 20 Employees
Here's where things get specific. Whether you can safely delay Medicare Part B depends largely on how many people work for your employer (or your spouse's employer, if you're covered under their plan).
If your employer has 20 or more employees, your group health plan is considered "primary," meaning it pays first before Medicare would. In this situation, you can absolutely delay enrolling in Part B without penalty. Your employer coverage is doing the heavy lifting, and Medicare is fine waiting in the wings.
If your employer has fewer than 20 employees, Medicare becomes the primary payer: even if you're still covered by your employer's plan. In this case, you need to enroll in Part B when you turn 65, or you risk facing both coverage gaps and late enrollment penalties.
Confusing, right? The size of your employer literally determines whether you can postpone one of the most important healthcare decisions you'll make.
When You Can (and Should) Wait
If you meet these criteria, you can confidently delay Part B:
- You're actively working (not retired, not COBRA, not retiree coverage)
- Your employer has 20 or more employees
- You have group health insurance through that employer (or your spouse's employer)
- You're happy with your current coverage
In this scenario, there's usually no reason to sign up for Part B right away. You'd be paying premiums for coverage that's essentially sitting on the bench while your employer plan handles your medical costs.
You'll enroll in Part B later: when you retire or when your employer coverage ends: using what's called a Special Enrollment Period. More on that in a minute.
When You Absolutely Must Enroll
Not everyone gets the luxury of waiting. You need to sign up for Part B during your Initial Enrollment Period (the seven-month window around your 65th birthday) if:
- You're not working
- Your employer has fewer than 20 employees
- You only have COBRA coverage
- You have retiree health benefits (even if your former employer is paying for it)
- Your employer coverage is ending
- You don't have any employer coverage at all
Missing this window without a valid reason triggers a late enrollment penalty that sticks with you for as long as you have Part B. That penalty is 10% of the Part B premium for each full 12-month period you could have had Part B but didn't sign up.
So if you wait three years to enroll without qualifying for an exception, you're looking at a 30% premium increase. Every month. For life. That's not a slap on the wrist: it's a permanent financial hit.
The Special Enrollment Period: Your Safety Net
Let's say you've been working past 65 with qualifying employer coverage. Eventually, one of two things will happen: you'll retire, or your employer coverage will end. When that moment arrives, you have an eight-month Special Enrollment Period to sign up for Part B without penalty.
This eight-month window starts the month after your employment ends OR the month after your group health coverage ends: whichever happens first.
Here's what's crucial: You need to enroll during those eight months. If you let that window close, you're back to facing penalties, and you'll have to wait until the next General Enrollment Period (January 1 – March 31) to sign up. Your coverage wouldn't start until July 1, leaving you with a potentially dangerous gap.
How to Prove You Had Credible Coverage
When you finally do enroll in Part B after delaying, Social Security will want proof that you had qualifying employer coverage. You'll need a letter from your employer (or your spouse's employer) that includes:
- Your name and the name of the person through whom you had coverage
- The dates you were covered under the group health plan
- The name of the employer providing the coverage
- Confirmation that the coverage was based on current employment
Don't wait until the last minute to request this documentation. Employers can sometimes be slow with paperwork, and you don't want administrative delays to push you past your enrollment deadline.
Common Mistakes Working Seniors Make
After helping thousands of people navigate this decision, I've seen the same mistakes pop up again and again:
Assuming COBRA counts as employer coverage. It doesn't. If you're on COBRA when you turn 65, you need to enroll in Part B during your Initial Enrollment Period.
Thinking retiree coverage qualifies. It doesn't matter if your former employer is being generous and providing health benefits in retirement: Medicare considers this secondary coverage. You need Part B.
Not understanding the small employer rule. Just because you have "employer coverage" doesn't mean you're exempt from enrolling. The 20+ employee threshold is non-negotiable.
Waiting too long after coverage ends. That eight-month Special Enrollment Period moves quickly. If you retire in March, you need to have Part B paperwork submitted by November at the latest.
Forgetting about Part A. While this post focuses on Part B, remember that most people should enroll in premium-free Part A at 65 even if they're delaying Part B. Part A doesn't interfere with HSA contributions as long as you don't use it, though this is a complex area worth discussing with a tax professional.
What If You're Still Not Sure?
Look, this decision involves your specific employment situation, your health insurance benefits, your health status, and your financial picture. There's no one-size-fits-all answer.
If you're genuinely uncertain whether your coverage qualifies, you have a few options:
- Contact your HR department and ask directly whether your plan is primary or secondary to Medicare
- Call Medicare at 1-800-MEDICARE and describe your situation
- Talk with a licensed insurance agent who specializes in Medicare
The worst thing you can do is nothing. Making no decision is still making a decision: and it's usually the most expensive one.
The Bottom Line
If you're still working at 65 with solid group health coverage from an employer with 20 or more employees, you can delay Part B without penalty. Take advantage of that flexibility and save yourself the monthly premium.
But if you don't meet that criteria: if your employer is smaller, if you're on COBRA, if you're retired with retiree benefits: don't gamble with your financial future. Enroll in Part B during your Initial Enrollment Period and avoid those lifetime penalties.
And when the time finally comes to transition from employer coverage to Medicare, mark those dates on your calendar. You've got eight months to make the switch, and you don't want to miss that window.
Starting Medicare should give you peace of mind, not financial stress. Understanding these rules helps you make the choice that's right for your situation: without second-guessing yourself or leaving money on the table.
Need help figuring out your specific situation? We can walk you through it. Because you deserve to make this decision with confidence, not confusion.
