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 does not extend the usual employment-based Part B enrollment window. COBRA drug coverage may still be creditable for Part D; check the plan's notice rather than assuming the same rule applies to both parts.

Special Enrollment Period (SEP)

If you qualify through group health coverage based on current employment, you generally have an 8-month Part B Special Enrollment Period after employment or that coverage ends, whichever happens first. COBRA does not extend it, and Part D has a separate deadline.

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 payment order and Part B enrollment eligibility with HR; separately request the drug plan's creditable-coverage notice
• Check your Part B and Part D enrollment deadlines separately before retirement
• Stop HSA contributions at least 6 months before enrolling in Medicare, if applicable