I thought I could just stay on my employer plan forever — why is Medicare so complicated?

Medicare was designed with the assumption that most people retire at 65. The rules about employer coverage are exceptions to handle people who keep working. The 20-employee threshold comes from federal coordination-of-benefits rules established decades ago.

What if I work for multiple employers or have multiple coverage sources?

The largest employer's employee count typically governs which insurance is primary. If you have coverage through multiple sources, contact Medicare (1-800-MEDICARE) for guidance on your specific situation.

I'm 67 and just realized I should have enrolled in Part B two years ago. What do I do?

Enroll immediately through the General Enrollment Period (January 1 – March 31) or, if your employment is ending, use your Special Enrollment Period. You'll pay the late penalty, but delaying further makes it worse. Also check whether you might qualify for Medicare Savings Programs to help with costs.

My employer says we have exactly 20 employees — which rule applies?

20 or more triggers the "large employer" rules. With exactly 20 employees, your employer coverage is primary and you can delay Part B.

I Have Employer Coverage and Still Working at 67, Should I Sign Up for Medicare?

Turning 65 while still working with employer health insurance creates one of Medicare's most confusing situations. The answer depends on a critical factor: how many employees does your employer have? Getting this wrong can cost you thousands in late penalties or coverage gaps.

The Short Answer

Employer Size	What You Should Do
20+ employees	Can delay Medicare Part B without penalty
Under 20 employees	Should enroll in Medicare when first eligible

Why it matters: Employer size determines which insurance pays first (primary) and which pays second (secondary). Making the wrong choice can leave you with minimal coverage or permanent financial penalties. Use our employer coverage lookup tool to verify your situation.

The 20-Employee Rule Explained

Large Employer (20+ Employees)

When you work for an employer with 20+ employees:

Employer insurance is primary — It pays first
Medicare is secondary — It pays what's left (if you have it)
You CAN delay Part B — No penalty when you eventually enroll
Part A is often worth enrolling in — It's free and helps with hospital costs

What this means for you: Your employer coverage works like it always has. Medicare is optional while you're working and covered.

Small Employer (Under 20 Employees)

When you work for an employer with fewer than 20 employees:

Medicare is primary — It pays first
Employer insurance is secondary — It only pays what Medicare doesn't
You MUST enroll in Part A and Part B — Delaying Part B triggers late penalties
Without Medicare, you're underinsured — Employer coverage alone won't pay claims properly

Warning: If you only have employer coverage without Medicare at a small employer, claims may be denied or underpaid because Medicare was supposed to be your primary insurance.

2026 Part B Costs and Late Penalties

If You Should Enroll

Part B premium for 2026: $202.90/month (standard rate)
Part B deductible: $283/year

If You Delay Improperly

The late enrollment penalty is 10% added to your premium for each 12-month period you should have had Part B but didn't. This penalty is permanent.

Example: You're 67, work for a small employer, and delayed Part B for 2 years:

Penalty: 20% of the standard premium
2026 premium: $202.90 + $40.58 = $243.48/month (for life)

How to Determine Employer Size

Count all employees, not just at your location:

Include full-time employees
Include part-time employees
Include employees at all company locations
Count based on 20+ weeks in the current or preceding year

Ask your HR department: “Does our company have 20 or more employees for Medicare coordination purposes?” You can also use our employer coverage lookup for guidance.

Get it in writing: If you're close to the threshold, documentation protects you.

What About Your Spouse's Employer Coverage?

The rules apply to coverage through your spouse's employer too:

Spouse works for large employer (20+): You can delay Part B while covered
Spouse works for small employer (under 20): You need to enroll in Part B

The test: Is the coverage based on current employment at a company with 20+ employees?

Part A Considerations

Part A is usually free if you or your spouse worked 40+ quarters. Even with employer coverage, enrolling in Part A often makes sense:

Reasons to Enroll in Part A While Working

No cost (premium-free for most)
Provides backup hospital coverage
May help with employer plan gaps

Reason to Possibly Delay Part A

You have a Health Savings Account (HSA): Part A enrollment disqualifies you from making new HSA contributions. If maximizing HSA contributions is a priority, you might delay Part A.

Warning: Part A enrollment can be retroactive up to 6 months. If you're claiming Social Security at 65+, you may be automatically enrolled in Part A.

The HSA Complication

If you have a High Deductible Health Plan (HDHP) with an HSA:

HSA contributions must stop once you enroll in any part of Medicare
Part A enrollment triggers this — even if you're still working
Planning matters: You can stop HSA contributions while keeping your HSA funds

Example Strategy

Stop HSA contributions 6 months before enrolling in Part A
Enroll in Part A when you turn 65
Keep employer HDHP until you retire
Enroll in Part B when employment ends

What Happens When You Stop Working

When your employment or employer coverage ends:

Special Enrollment Period (SEP)

Track your Special Enrollment Period deadline →

8 months to enroll in Part B without penalty
Clock starts when employment OR coverage ends (whichever is first)
Don't wait until the last month — apply early to avoid coverage gaps

Documents You'll Need

CMS-L564: Request for Employment Information (your employer completes this)
CMS-40B: Application for Enrollment in Medicare Part B
Proof of employment dates and coverage

Timeline Example

Date	Event
June 1, 2026	You retire, employer coverage ends
June 1 – January 31, 2027	Your 8-month SEP
Best practice	Apply by July 2026 for August 1 Part B start

COBRA Coverage Warning

COBRA is NOT the same as active employment coverage:

COBRA does not extend your SEP
COBRA does not count as “coverage based on current employment”
If you take COBRA instead of enrolling in Medicare, late penalties may apply

Recommendation: When employment ends, enroll in Medicare — don't rely on COBRA to delay enrollment.

Retiree Coverage Considerations

Retiree coverage also differs from active employment coverage:

Retiree insurance typically expects you to have Medicare
Many retiree plans are secondary to Medicare by design
Not enrolling in Medicare while on retiree coverage can leave you underinsured

Ask your former employer: “Does the retiree plan require Medicare enrollment?”