Working Past 65: Should You Enroll in Medicare or Keep Employer Coverage?

The Big Question at 65: Enroll or Delay?

If you have group coverage through a job you (or your spouse) are still actively working at, Medicare rules give you real flexibility. You are generally allowed to delay enrollment in Part B and use a Special Enrollment Period (SEP) later without a late penalty, or sign up at any time while you are still covered by that group plan.

But "you can delay" is not the same as "you should delay." The right choice depends on three things:

1. How many employees your employer has
2. Whether you (or your spouse) contribute to an HSA
3. How your current plan's costs compare to Medicare plus a Medigap policy

Before you decide, ask your HR or benefits administrator two questions in writing: Is my coverage considered primary or secondary once I turn 65, and does the drug plan qualify as creditable coverage for Medicare Part D?

Who Pays First: The Employer Size Rule

Medicare's coordination-of-benefits rules turn on a single number: 20. If your employer has 20 or more employees, the group plan pays first and Medicare pays second. If your employer has fewer than 20 employees, Medicare pays first and the group plan pays second.

This matters because if Medicare is supposed to be primary and you never enrolled, your employer plan can pay as if Medicare had already paid its share, leaving you responsible for large bills.

Large employer (20+ employees)

• Your group plan pays first, Medicare pays second.
• The employer must offer the same benefits on the same terms to workers 65+ as to younger workers, and cannot push you off the plan or offer incentives to drop it.
• You can safely delay Part B without a late enrollment penalty and use the 8-month SEP when work or coverage ends.

Small employer (fewer than 20 employees)

• Medicare pays first, the group plan pays second.
• Small-employer coverage is generally not treated as coverage that allows you to delay Part B safely.
• The safer approach is to enroll in Part A and Part B during your Initial Enrollment Period (the 7-month window around your 65th birthday) and keep the employer plan as secondary.

Should You Take Premium-Free Part A?

Most workers qualify for premium-free Part A because they have paid Medicare taxes for at least 40 quarters (about 10 years). Because there is no monthly premium, the default advice is usually to enroll in Part A at 65 even if you keep your employer coverage. It can act as secondary hospital insurance behind your group plan.

There is one big exception: HSA contributions.

The HSA conflict rule

Once you enroll in any part of Medicare (including premium-free Part A), you can no longer contribute to a Health Savings Account for the months you are covered. This is true even if you are still working and still on your employer's HSA-qualified high-deductible plan. Employer contributions to your HSA must also stop.

Worse, when you enroll in Part A after 65, coverage is back-dated up to 6 months (but never earlier than the month you turned 65). Any HSA contributions in those retroactive months become excess contributions subject to a 6% excise tax per year until corrected.

Most experts recommend stopping HSA deposits at least 6 months before enrolling in Part A or filing for Social Security (which auto-enrolls you in Part A).

If you do not contribute to an HSA, taking Part A at 65 is usually the easy call. If you do, delaying Part A (and Social Security) while you stay on an HSA-qualified plan preserves those tax-free contributions.

Delaying Part B and the 8-Month Special Enrollment Period

Part B costs $202.90 per month in 2026 for most people, so most workers with strong employer coverage delay it. The rule that makes this safe is the Special Enrollment Period.

How the SEP works

If you (or your spouse) had group coverage based on current employment, you get 8 months to enroll in Part B without a penalty once that job or coverage ends. The clock starts the earlier of the month after employment ends or the month after active coverage ends, whichever comes first.

If you enroll while still working or within the first month after coverage ends, you can choose a Part B effective date up to 3 months in the future, which helps you line up a clean handoff to Medicare.

The Part B late enrollment penalty

Miss the SEP and Medicare adds 10% to your Part B premium for every full 12-month period you could have been enrolled but weren't (excluding months you had qualifying current-employer coverage). On the 2026 base premium of $202.90, that is $20.29 per year of delay, added to your bill for life.

For a deeper breakdown of the 2026 premium and how it interacts with Medigap, see our guide to the best Medicare Supplement plans of 2026.

COBRA, Retiree Coverage, and TRICARE: How They Coordinate

When you retire or leave your job, you may be offered other coverage that seems to replace employer insurance. Here is how each option coordinates with Medicare.

COBRA

COBRA lets you keep your former employer's plan for a limited time, but Medicare treats you as if you no longer have active employer coverage. That means:

• COBRA does not extend your Part B SEP. The 8-month clock still starts when your active job or coverage ends, not when COBRA ends.
• If you have COBRA and are Medicare-eligible but not enrolled, COBRA may pay only a small share of your bills.
• Most COBRA plans end or become secondary once you enroll in Medicare.

Retiree health coverage

Retiree coverage is different from COBRA. It is ongoing group coverage from a former employer or union. Once you are retired and enrolled in Medicare:

• Medicare pays first.
• Retiree coverage pays second, usually helping with deductibles, coinsurance, and services Medicare doesn't cover.

Retiree coverage does not protect you from the Part B penalty either, so you still need to enroll in Part B on time.

TRICARE For Life (TFL)

Military retirees switch from traditional TRICARE to TRICARE For Life at 65. TFL requires you to have both Medicare Part A and Part B, and you will lose TRICARE if you skip or drop Part B. Once enrolled:

• Medicare pays first for TRICARE-covered services.
• TFL wraps around as secondary, covering most Medicare coinsurance and deductibles.
• TRICARE pharmacy is creditable coverage for Part D, so you can skip Part D without a penalty.

Most TFL beneficiaries do not need Medigap or Medicare Advantage on top, because TFL already fills the gaps in Original Medicare.

The Transition: Employer Plan to Medicare + Medigap

When you finally retire, the goal is a seamless handoff: employer plan ends on day one, Medicare starts on day one, and a Medigap policy starts on day one. Here is the sequence.

Step 1: Set your Part B effective date

As soon as you have a firm end date for employer coverage, use your 8-month SEP to enroll in Part B. Aim to have Part B effective the first of the month after your group plan ends (or the same month, if allowed).

Step 2: Apply for Medigap while still in your window

Your 6-month Medigap Open Enrollment Period starts the first month you are both 65+ and enrolled in Part B. Because you delayed Part B, your Medigap OEP was also delayed and starts fresh when Part B kicks in.

During that 6-month window, insurers must accept you at the best rate regardless of your health. You can apply in advance and request that the Medigap policy start the same day Part B does. For the mechanics of that window, see our Medicare Supplement Open Enrollment guide.

Step 3: Pick a plan letter

Plan G is the top pick for most people new to Medicare in 2026, covering nearly everything after the $283 Part B deductible. Plan N costs less and works well if you can handle small office copays. Compare all lettered plans in our Medigap comparison chart, or read the deep dive on Plan G coverage and costs.

Step 4: Add Part D (or confirm creditable drug coverage)

If your employer drug plan was creditable and ends within 63 days, you have a 2-month SEP to join a Part D plan without a penalty. TRICARE members can skip this step.

For a broader look at the full enrollment process from Initial Enrollment through Medigap purchase, see our first-time Medicare enrollment guide. If you live in a state with additional Medigap protections, our guide to Medicare Supplement plans by state covers birthday-rule and guaranteed-issue windows that may give you a second chance later.

Frequently Asked Questions

Do I need Medicare if I have employer insurance at 65?

If your employer has 20 or more employees, you generally do not need to enroll in Part B right away, because the group plan pays first. Most people still enroll in premium-free Part A unless they contribute to an HSA. If your employer has fewer than 20 employees, Medicare is primary, and you should enroll in both Part A and Part B during your Initial Enrollment Period to avoid coverage gaps.

Can I contribute to an HSA if I enroll in Medicare Part A?

No. Enrollment in any part of Medicare, including premium-free Part A, ends your ability to make new HSA contributions for those months. Part A also back-dates up to 6 months when you enroll after 65, which can turn recent contributions into excess contributions subject to tax penalties. Most advisors recommend stopping HSA deposits at least 6 months before you plan to enroll in Part A or claim Social Security.

Does COBRA count as creditable coverage for Medicare?

Not for Part B. Only coverage from a current, active employer counts for the Part B Special Enrollment Period, so COBRA will not extend your enrollment window or stop the late enrollment penalty. For Part D drug coverage, COBRA may or may not be creditable depending on the plan design, so ask the plan administrator for a Notice of Creditable Coverage. Enroll in Part B as soon as your active job or coverage ends, regardless of whether you elect COBRA.

When does my Medigap Open Enrollment Period start if I delayed Part B?

Your 6-month Medigap Open Enrollment Period begins the first month you are both 65 or older and enrolled in Part B. If you delayed Part B while working past 65, your Medigap OEP is also delayed and starts fresh when Part B becomes effective. During this window, insurers must accept you regardless of health status and cannot charge more due to pre-existing conditions.

What is the Part B late enrollment penalty in 2026?

The penalty adds 10% to your Part B premium for each full 12-month period you were eligible but not enrolled and did not have qualifying current-employer coverage. In 2026, the base Part B premium is $202.90, so each year of delay adds $20.29 per month to your bill. The penalty is permanent for as long as you have Part B, which is why enrolling during your Initial Enrollment Period or Special Enrollment Period matters so much.