Working past 65: how Medicare fits with employer coverage

Last reviewed: September 2026

Does employer size matter?

It depends on your employer’s size. If your employer has 20 or more employees, your group health plan generally pays first, and many people can delay Part B — and Part A, if they’d pay a premium for it — without a penalty. If your employer has fewer than 20 employees, Medicare generally pays first, so you usually need Parts A and B when you’re first eligible to avoid gaps in your coverage.

Coverage has to be current

The coverage has to be based on current employment — yours or your spouse’s. COBRA and retiree coverage don’t count for this purpose.

Your Special Enrollment Period for Part B

You can sign up for Part B any time you’re covered by a group health plan based on current employment, or during the 8 months that begin the month after the employment or the coverage ends, whichever happens first. When you apply, your employer typically completes a form confirming your coverage (CMS-L564), submitted along with the Part B application (CMS-40B).

HSAs and Medicare

Once you’re enrolled in any part of Medicare, including Part A, you can no longer contribute to a Health Savings Account (HSA). If you sign up for Medicare, or Social Security, after 65, premium-free Part A coverage can be retroactive up to 6 months — but not earlier than the month you turned 65. To avoid a tax penalty, plan to stop HSA contributions 6 months before you apply.

You can still use money already in your HSA for qualified medical expenses, including Medicare Part B, Part D, and Medicare Advantage premiums — but not Medigap premiums.

Check your drug coverage

Ask your employer whether your prescription drug coverage is creditable — meaning at least as good as Medicare’s. Knowing this now can help you avoid a Part D penalty later.

Your Medigap timing

Your Medicare Supplement (Medigap) Open Enrollment Period starts when you enroll in Part B. Delaying Part B while you have employer coverage also delays, and preserves, that window for later.

Is it worth comparing costs?

In some cases, Medicare plus a Medigap or Medicare Advantage plan may cost less than your share of an employer plan, especially if you’re also covering a spouse. It’s worth running the numbers for your specific situation rather than assuming either option is better.

This guide is general information, not tax advice. Talk with your HR department or a tax professional about your specific situation.

How I can help

Deciding whether to keep employer coverage or move to Medicare is rarely simple. I’ll help you compare your options side by side. Schedule a review to talk it through.