AVW Insurance | Medicare Guides & Free Resources

If you still have health coverage through work, a spouse, or retiree benefits, you’ve probably asked, “Who pays first once I have Medicare?”

I get that question almost every week. The answer depends on what type of insurance you have and who provides it. Let’s go through the basics step by step so you don’t get surprised by a bill later.

What Is Medicare Coordination of Benefits?

Medicare calls this process Coordination of Benefits (COB). It decides which plan pays first when you have more than one type of insurance.

This matters because it affects what your doctor bills and how much you owe.

If you’d like a quick refresher on how Medicare itself works, read my post Medicare 101: What to Know Before Choosing a Plan

How Medicare Works with Employer or Retiree Insurance

If you’re 65 or older and still covered through an employer plan, the rule depends on company size.

• 20 or more employees: your employer plan pays first, and Medicare pays second.
• Fewer than 20 employees: Medicare pays first.

This one detail can prevent billing headaches.

I’ve talked with people who skipped enrolling in Part B because they assumed their work plan handled everything, only to find out Medicare should have been primary.

Check this before your 65th birthday or before you retire.

Download the Free Medicare Starter Kit to get a checklist of what to confirm with your HR department.

Coordination of Benefits Rules You Should Know

If you’ve already retired, your retiree coverage becomes secondary. Medicare pays first, and your retiree plan picks up the rest.

Some retiree plans offer drug coverage that’s considered “creditable,” which means it’s as good as Medicare’s Part D.

If it’s not, you could face a penalty later for skipping Part D. Every fall, review your retiree plan notice. It will tell you if your drug coverage is creditable.

For a deeper breakdown of costs, read 3 Medicare Costs You Need to Double-Check Before AEP Ends.

Coverage Through a Spouse

1. If you’re covered under your spouse’s employer plan, the same company-size rule applies.
2. Ask the employer whether their plan pays first or if Medicare does.
3. It’s a two-minute call that can save hours of paperwork later.

Other Common Insurance Types

Here’s how Medicare coordinates with a few other plans I see often:

• TRICARE: Medicare pays first for most services; TRICARE fills in afterward.
• COBRA: Once you have Medicare, COBRA becomes secondary.
• Marketplace plans: Once you enroll in Medicare Part A and B, you should cancel your Marketplace plan. You can technically keep it, but you’ll lose any premium tax credits and end up paying the full cost. If you’re delaying Part B because you still have employer coverage, you can keep your Marketplace plan until your Medicare starts, but the two do not work together on claims.
• Veterans benefits: You can have both, but they rarely work together on the same claim.

If you want a full guide that compares your choices, see the Guide to Medicare Choices

What to Do if Your Claims Are Delayed

If a doctor bills the wrong plan first, contact the provider’s billing office and confirm which plan should be primary.

If the issue continues, call the Benefits Coordination and Recovery Center (BCRC) at 1-855-798-2627 to verify your coordination details.

Always keep notes of who you spoke with and when.

Steps to Take When You Have Multiple Plans

1. Contact each plan and confirm who pays first.
2. Ask for written confirmation.
3. Keep a copy with your Medicare card.
4. Review the payer order every year or whenever your job status changes.

Here’s a real example:

I once helped a client who was still working at age 68. His employer had 50 employees, so his group plan paid first.

When he retired the next year, Medicare automatically became his primary payer. I helped him understand what to expect and how to notify both plans so his claims would process correctly from day one.

You can do the same by checking early.

Key Takeaways

• Always confirm which plan pays first.
• Review your retiree or employer coverage each year.
• Don’t rely on assumptions—rules differ by company size and plan type.
• Keep everything in writing.

Next Step

If you’re not sure how your coverage fits with Medicare, start with the Free Medicare Starter Kit.
It includes a Coordination of Benefits Checklist and a simple guide so you know exactly what to ask your HR or benefits department.

Resources and References

• Medicare.gov – Coordination of Benefits Overview
• SSA.gov – Working Past 65

Disclaimer

This content is for educational purposes only and does not constitute official Medicare advice. I am not affiliated with Medicare or any government agency. For complete coverage options, visit Medicare.gov or call 1-800-MEDICARE.

Examples shared are general scenarios for educational purposes and do not reflect any specific individual or situation. This content does not provide plan recommendations or enrollment guidance.