Working Past 65: When to Enroll in Medicare

If your employer has 20 or more employees and you are covered by their health plan, your employer plan is the primary payer. Medicare is secondary. You can delay Part B enrollment without penalty as long as you remain covered by active employer insurance. When that coverage ends, you have an 8-month Special Enrollment Period to enroll in Part B.

The 20-employee threshold is based on the total number of employees across your employer's entire organization, not just your location or department. If you are unsure, ask your HR department directly.

If your employer has fewer than 20 employees, Medicare becomes the primary payer for your healthcare costs at age 65, even if you have employer-sponsored insurance. Your employer plan is designed to pay after Medicare has paid its share. If you have not enrolled in Medicare, your employer plan may calculate its payment as if Medicare had already paid, leaving you responsible for the portion Medicare would have covered. For small-employer workers, the recommendation is clear: enroll in Medicare Part A and Part B during your Initial Enrollment Period at 65. Use our Medicare Eligibility Checker to confirm your eligibility before your birthday month.

Part A (hospital insurance) is premium-free for most people who have worked and paid Medicare taxes for at least 10 years (40 quarters). There is generally no reason to delay Part A enrollment. It costs nothing and provides a secondary layer of hospital coverage. The one exception: if you contribute to a Health Savings Account (HSA), see the section below before enrolling. For a full breakdown of what Part A and Part B cover, see our Medicare 101 overview.

Part B (medical insurance) costs $202.90 per month in 2026 for most people. As long as you remain covered by your employer's active group health plan, you can delay Part B enrollment without incurring a late enrollment penalty. You do not need to sign up during your Initial Enrollment Period.

When you eventually enroll in Part B via your Special Enrollment Period, you will need to prove you had qualifying employer coverage. Keep your insurance cards, employer benefits statements, and any letters confirming your coverage dates. Your HR department can provide a letter confirming your coverage period.

If you are already receiving Social Security benefits, you may be automatically enrolled in both Part A and Part B at 65. If you want to delay Part B, you must actively decline it. Contact Social Security at 1-800-772-1213 before your 65th birthday to decline Part B enrollment.

When you apply for Social Security benefits, Medicare Part A enrollment is retroactive by up to 6 months. If you have been contributing to an HSA during those 6 months, those contributions become excess contributions, subject to income tax and a 6% excise tax penalty. If you plan to delay Social Security past 65 to protect your HSA, do not apply for Social Security until you are ready to stop HSA contributions.

If you are not contributing to an HSA, enroll in Part A at 65. It is free and provides additional hospital coverage. If you are contributing to an HSA and want to continue, delay Part A enrollment and do not apply for Social Security. If you are ready to stop HSA contributions, enroll in Part A and coordinate the timing carefully with your employer's HR department to avoid excess contribution penalties.

Processing times can vary, and you want your Part B coverage to start as close to your employer coverage end date as possible to avoid a gap in coverage. Enrolling in the first month or two of your SEP gives you the most flexibility and the smoothest transition.

If your spouse's employer has 20 or more employees and you are covered as a dependent on their plan, you qualify for the same SEP protections. You can delay Medicare Part B without penalty as long as you remain covered under your spouse's active employer plan. When your spouse retires or loses coverage, your 8-month SEP begins. See our Medicare Enrollment Timeline for a full breakdown of all enrollment windows.

John retires at 65 in January. His employer coverage ends January 31. He elects 18 months of COBRA. His 8-month SEP runs February through September. If John waits until his COBRA expires in July of the following year to enroll in Part B, he has missed his SEP by 10 months. He will face a permanent 10% Part B penalty and must wait for the General Enrollment Period (January 1 through March 31) with coverage starting July 1.

If you are considering COBRA, enroll in Medicare Part B first, then use COBRA only to bridge any gap in coverage for services Medicare does not cover, such as dental or vision. Do not use COBRA as a substitute for Medicare enrollment.

Active employer group plan coverage from an employer with 20 or more employees qualifies. Coverage as a dependent on a spouse's employer plan from an employer with 20 or more employees also qualifies. Individual marketplace plans, COBRA, retiree health coverage, and self-purchased insurance do not qualify. When in doubt, confirm with your HR department or a licensed Medicare specialist before making your enrollment decision. For a side-by-side look at how Original Medicare and Medicare Advantage handle cost-sharing differently, see our Medicare Costs at a Glance guide.