If you're 65 or older and still working, you're probably juggling two health plans: Medicare and your employer's coverage. Coordination of benefits (COB) rules decide which plan pays first. Get the rules right and you maximize coverage and cut out-of-pocket costs. Get them wrong and you could overpay or face penalties.
Understanding the "Payer of First Resort" Rules
The primary question is: which plan pays your medical bills first? The answer depends mainly on the size of your employer and whether you're actively working.
If Your Employer Has 20 or More Employees
When your employer has 20 or more workers, the group health plan pays first. Medicare is secondary, stepping in after your employer plan has paid its share to cover some deductibles, copays, and coinsurance. That can slash your out-of-pocket costs.
If Your Employer Has Fewer Than 20 Employees
For companies with fewer than 20 employees, it's the opposite: Medicare pays first, the employer plan second. Check with your HR department, since some small plans have edge cases.
Both rules apply while you're actively working. Retiree coverage and COBRA are different: for people 65 or older, Medicare pays first with either one, and COBRA does not extend your window to sign up for Part B.
Key Decisions You Have to Make
Your Initial Enrollment Period, the seven-month window around your 65th birthday, is a high-stakes moment. Here's what to weigh:
- Part A (Hospital Insurance): Usually free, so most people sign up right away even if they have employer coverage. It adds a second layer of protection.
- Part B (Medical Insurance): Comes with a monthly premium. If you have group health coverage through current employment, your own or your spouse's, you can delay Part B without penalty. Just remember: you have an 8-month Special Enrollment Period after that employment or coverage ends, whichever comes first, or you'll owe a late-enrollment penalty for life.
- Part D (Prescription Drug Coverage): Delay Part D only if your employer plan offers creditable prescription drug coverage. Your employer must send you a Creditable Coverage notice every year, so hold onto it.
- HSAs and Delaying Enrollment: Want to keep contributing to an HSA? You can't if you're on Medicare, any part of it. Stop HSA contributions at least six months before applying for Social Security or Medicare, since Part A can be backdated up to six months and contributions made in that window can face a 6% excise tax.
The Strategic Opportunity: A Health-to-Wealth Approach
Most coordination of benefits is reactive, settling who pays after the fact. A forward-thinking approach, like the one from WellthCare, treats this moment as a chance to improve health and build wealth at the same time. WellthCare, the first Health-to-Wealth Benefit System, keeps employees inside a prevention-first ecosystem even after they turn 65, rewarding every verified health action with store dollars and automatic retirement contributions.
For employers, guiding eligible employees into an integrated Medicare solution like WellthCare Medicare™ delivers smart cost control on top of compliance. Employees stay inside a familiar system at 65 instead of falling off a cliff, which reduces employer claim exposure over time. They keep perks like the WellthCare Store™ for rewards and automatic retirement contributions for healthy habits.
MSP Rules: No Financial Incentives to Drop Coverage
Cost control has a hard legal boundary here. Medicare Secondary Payer rules prohibit employers from offering Medicare-eligible employees financial or other incentives to drop the group health plan or skip enrollment. That includes reimbursing Part B or Part D premiums, paying for a Medicare Supplement or Medicare Advantage plan, or offering cash rewards to waive coverage. Violations can trigger civil money penalties. Employees may still decline coverage on their own, but the decision has to be theirs, not something an employer pays them to make.
What to Do Next
- Start talking early. HR should begin conversations 6 to 12 months before an employee turns 65. Share clear rules, creditable coverage notices, and sign-up resources.
- Get the facts. Employees should call the Medicare Benefits Coordination & Recovery Center (BCRC) and check with their benefits admin to confirm who pays first.
- Look into integrated solutions. HR teams should explore ways to support employees through the Medicare transition without losing their connection to corporate wellness programs. That keeps care smooth, boosts retention, and saves money.
- Document everything. Creditable coverage notices, enrollment forms, emails. It's your safety net against future penalties.
Being eligible for both Medicare and an employer plan is a turning point for your health and finances. Get the rules straight and use modern tools, and both employees and employers come out ahead: healthier now, wealthier later, and spending smarter.