Turning 65 while still working and covered by employer health insurance is one of the most misunderstood situations in Medicare. Many Californians assume they can simply wait, or that their employer plan protects them automatically. Getting the timing wrong results in permanent premium penalties or coverage gaps that leave you paying large medical bills out of pocket. This guide lays out exactly what you need to know in 2026.
The Core Rule: Company Size Determines Everything
How Medicare coordinates with your employer plan depends almost entirely on how many people your employer has on payroll. This number determines who pays first when you receive medical care and whether you can safely delay Medicare enrollment.
Part A: Enroll at 65 in Almost Every Case
Part A covers hospitalizations, skilled nursing facility care, and some home health services. For most people who have worked and paid Social Security taxes for 10 or more years, Part A has no monthly premium. Because it costs nothing, it generally makes sense to enroll in Part A at 65 even if you keep your employer plan. Part A can act as secondary coverage for hospital costs, potentially reducing your out-of-pocket expenses.
Part B: When to Enroll and When You Can Wait
Part B covers doctor visits, outpatient services, durable medical equipment, and many other services. It has a monthly premium of $185 for most people in 2026.
If You Work for an Employer with 20 or More Employees
You can delay Part B enrollment while you have active employer coverage. When you stop working or lose that coverage, you have an 8-month Special Enrollment Period to enroll in Part B without penalty. Enroll within those 8 months. Miss the window and you will wait for the General Enrollment Period (January through March), coverage will not begin until July, and you will pay a permanent late enrollment penalty.
If You Work for an Employer with Fewer Than 20 Employees
You must enroll in Part B at 65. By law, Medicare is the primary payer in this situation. If you are not enrolled, Medicare pays nothing. The employer plan, as the secondary payer, can refuse to pay the portion Medicare was supposed to cover. The result: you pay those bills out of pocket.
The COBRA Trap: A Costly Misunderstanding
When someone retires or loses a job, COBRA continuation coverage is often available for up to 18 months. Many people assume that COBRA counts as employer coverage for Medicare purposes and delays the enrollment requirement. It does not.
The correct approach at retirement: enroll in Medicare Parts A and B within 8 months of losing active employer coverage. COBRA may still be useful for covering dependents, but it does not protect you from Medicare enrollment requirements.
Coordination of Benefits: Who Pays What
| Situation | Primary Payer | Secondary Payer | Your Cost |
|---|---|---|---|
| Working at employer with 20+ employees, active employer coverage | Employer plan | Medicare (if enrolled) | Only your employer plan copay/deductible |
| Working at employer with fewer than 20 employees | Medicare | Employer plan | Part B deductible plus coinsurance, reduced by employer plan |
| Retired with Medicare and COBRA | Medicare | COBRA | Only COBRA coinsurance/copay after Medicare pays |
| Retired with Medicare only | Medicare | Medigap plan (if enrolled) | Minimal or none with a strong Medigap plan |
Prescription Drug Coverage (Part D)
Employer plans often include prescription drug coverage. If that coverage is "creditable" (at least as good as Medicare Part D), you can delay Part D enrollment without penalty while you have that employer coverage. Your employer must notify you each year whether your drug coverage is creditable.
If your employer drug coverage is not creditable, or you lose it, you have 63 days to enroll in a Part D plan without penalty. After 63 days without creditable coverage, the Part D late enrollment penalty applies permanently.
Recommended Timeline for Californians Approaching 65
| When | What to Do |
|---|---|
| 3 months before turning 65 | Confirm employer size (20 or more vs. fewer than 20 employees). Ask HR whether your drug coverage is creditable. |
| At 65 (employer with 20+ employees) | Enroll in Part A if no active HSA. You may delay Part B and Part D if employer coverage is creditable. |
| At 65 (employer with fewer than 20 employees) | Enroll in Parts A and B immediately. Evaluate whether to also enroll in Part D or rely on employer drug coverage. |
| When you retire or lose employer coverage | Enroll in Part B within 8 months. Do not wait for COBRA to end before enrolling in Medicare. |
| After enrolling in Medicare at retirement | Compare Medicare Advantage plans or Medigap supplements. Choose a Part D plan if you have no other creditable drug coverage. |
The Late Enrollment Penalty: What the Math Looks Like
The Part B penalty is 10% added to the premium for every 12 months you should have enrolled but did not. It is permanent. The 2026 standard premium is $185 per month. A two-year delay without qualifying coverage adds 20%, which is $37 per month for life. Over 10 years, that is more than $4,400 in avoidable costs.
The Part D penalty is 1% of the national base beneficiary premium per month without creditable coverage. Also permanent, added to your monthly Part D premium for life.
For California residents who also have Medi-Cal coverage, the coordination rules are different. Visit our sister site medicare-california.com for guides on dual-eligible benefits and Medicare Advantage options in California.
Frequently Asked Questions
Do I have to enroll in Medicare if I still have employer health insurance?
It depends on your employer's size. With 20 or more employees, you can delay Part B without penalty while on active employer insurance. With fewer than 20 employees, you must enroll in Parts A and B at 65 to avoid coverage gaps and denied claims from your employer plan.
Which insurance pays first, Medicare or employer coverage?
With 20 or more employees, employer insurance pays first and Medicare pays second. With fewer than 20 employees, Medicare pays first. This coordination rule is fundamental for submitting claims correctly and avoiding disputes.
What happens if I retire after 65 and lose my employer coverage?
You have an 8-month Special Enrollment Period to sign up for Part B penalty-free. Enroll within that window. If you wait longer, you may face months without Part B coverage and a permanent premium increase.
Can I use Medicare together with COBRA from my former employer?
Yes, both can be active simultaneously. When Medicare is already in effect, it pays first and COBRA pays second. COBRA does not count as active employer coverage, so it does not give you a Special Enrollment Period when it ends.
What is the Medicare Part B late enrollment penalty?
Ten percent of the standard Part B premium for every 12-month period you should have enrolled but did not. It is permanent. With a 2026 base premium of $185, a two-year delay costs $37 extra per month for the rest of your life.
Not sure how to coordinate Medicare with your employer coverage in California? Our bilingual licensed agents can review your specific situation at no cost and no pressure. One call can prevent years of unnecessary expenses.
Share this with someone you love. If a family member or friend is turning 65 and still working, this information could save them a lot of money and confusion.