Medicare and Still Working: How to Coordinate Medicare With Employer Insurance

Working past 65 is increasingly common — and it raises an important question: do you need Medicare if you already have employer insurance? The answer depends on the size of your employer and a few other factors. Get the enrollment-timing basics first in our Turning 65 enrollment timeline guide if you haven't already.

The Key Rule: Employer Size Matters

Whether you can safely delay Medicare while working comes down almost entirely to your employer's size:

• 20 or more employees: your employer insurance is primary and Medicare is secondary — you can generally delay Part B without penalty until that coverage ends.
• Fewer than 20 employees: Medicare typically becomes primary at 65 — you generally need to enroll in Part B on time, or your employer plan may pay very little for services Medicare would have covered.

COBRA and Medicare

Don't confuse COBRA with active employer coverage. COBRA extends your former employer's group plan after you leave, but it is not considered creditable coverage for Medicare enrollment purposes. If you're on COBRA at 65, you should generally enroll in Medicare to avoid a coverage gap and a future late enrollment penalty.

Special Enrollment Period (SEP)

When you lose employer coverage — by retiring or otherwise — you get an 8-month Special Enrollment Period to enroll in Part B without penalty. The SEP begins when your employment ends or your employer coverage ends, whichever comes first, not whenever you get around to signing up.

HSA and Medicare

You cannot contribute to a Health Savings Account once you're enrolled in any part of Medicare — including Part A, which can be retroactively effective up to 6 months before your enrollment date (but not before your 65th birthday) if you sign up after 65 and are also claiming Social Security. If you're planning to keep contributing to an HSA, stop contributions at least 6 months before you plan to enroll in Medicare or claim Social Security.

Coordination of Benefits

When you have both Medicare and employer insurance, claims flow to whichever plan is "primary" first, and the "secondary" plan may pick up some remaining costs. Getting this backward — for example, assuming Medicare is secondary when your small employer's plan actually requires Medicare to be primary — is one of the more common and expensive Medicare mistakes; see our guide on 7 Medicare mistakes that cost retirees thousands for more.

Retirement Planning Checklist

• Ask HR how many employees are covered under your group health plan
• Confirm in writing whether your coverage is considered "creditable" for Medicare purposes
• Mark your calendar for your 8-month SEP the moment you know your retirement date
• Stop HSA contributions at least 6 months before enrolling in Medicare, if applicable