COBRA and Medicare: the Mistake That Follows You for Life

The misunderstanding, stated plainly

There is a well-known rule that you can delay Medicare Part B without penalty if you are still covered by a group health plan through work. That rule is real, and it is the right advice for someone who is still employed at 65.

COBRA looks like that coverage. It is the same insurer, the same card, the same network, the same plan name. It is not the same thing legally. The exemption depends on coverage based on current employment, and COBRA by definition begins when the employment ends. Medicare therefore treats someone on COBRA the same as someone with no coverage at all for enrollment-timing purposes.

The clock you are actually on

When employment-based coverage ends, you get a Special Enrollment Period for Medicare Part A and Part B lasting eight months. It begins the month after your employment ends, or the month after the group coverage based on that employment ends, whichever happens first.

Read that last clause again, because it is the whole problem. Your employment ended first. So the clock starts then, and COBRA does nothing to pause it.

Nothing in that sequence produces a warning letter. The COBRA administrator is not responsible for your Medicare timing, and Medicare does not know you are on COBRA. The failure is silent until you try to enroll.

What the penalty actually costs

The Part B late enrollment penalty is 10% of the standard Part B premium for each full 12-month period you could have had Part B and did not. It is added to your premium for as long as you have Part B, which for most people means for life. It does not expire after a few years, and it rises as the standard premium rises, because it is calculated as a percentage rather than a fixed amount.

One missed year is a 10% surcharge. Two is 20%. Someone who rides an 18-month COBRA continuation to its end and only then enrolls can easily land in the first band, and depending on when the General Enrollment Period falls, in the second. Over a 20-year retirement, that is a large number attached to a decision that felt at the time like doing nothing.

There is a separate Part D penalty covering prescription drug coverage, calculated differently and triggered by going 63 days or more without creditable drug coverage. Your COBRA plan's drug benefit may or may not count as creditable. The plan is required to tell you which, so find that notice or ask the administrator directly. Do not assume.

The order in which things happen changes the rules

Two situations that sound similar are treated differently.

You are already on Medicare, then you lose your job

Being entitled to Medicare before you elect COBRA does not stop you from electing it. You can hold both. The question becomes whether the second policy is worth its price, which is discussed below.

You are on COBRA, then you become entitled to Medicare

Becoming entitled to Medicare after electing COBRA is one of the grounds on which a plan may terminate your COBRA coverage early. You do not necessarily get to keep both. This is why enrolling in Medicare on time and treating COBRA as the secondary question is the safer sequence for anyone near 65.

If you hold both, Medicare generally pays first

Coordination of benefits follows the same logic as the enrollment rules. Because COBRA is not coverage based on current employment, Medicare is normally the primary payer and COBRA is secondary.

The practical consequence is uncomfortable. Someone who delays Part B while paying a full COBRA premium can end up with claims processed as though Medicare had already paid its share, leaving the portion Medicare would have covered unpaid. You pay the full premium and still face the bill. If you are on COBRA and eligible for Medicare, being enrolled in Part B is what makes the arrangement work rather than an optional extra.

Do you even want COBRA on top of Medicare?

Once Medicare is primary, a full-price COBRA premium is buying you secondary coverage only, and there are usually cheaper ways to buy that. Before electing, weigh it against a Medicare Supplement (Medigap) policy or a Medicare Advantage plan, both of which are designed for the job.

One timing point deserves attention here: the window in which you can buy a Medigap policy with guaranteed issue, meaning no medical underwriting, is limited. Spending it on COBRA and shopping for Medigap 18 months later can mean facing underwriting with whatever health history you have accumulated in the meantime. If you are in this position, this is the single best reason to talk to a counsellor before electing.

COBRA can still be the right call, particularly where it covers dental and vision that Medicare does not, or where a spouse or dependent needs to stay on the plan. Just make it a decision rather than a default.

When it is your spouse who is going on Medicare

The mirror image of this problem hits couples with an age gap: the covered employee reaches 65, moves to Medicare, and the younger spouse loses the group plan they were riding on. That is a qualifying event in its own right, and it gives the spouse and dependents an independent right to continuation for up to 36 months rather than 18. The homepage covers that scenario in more detail, and the eligibility guide sets out how the 36-month events work.

What to do if you are 64 or older

1. Find the date your employment ended, not the date your coverage ended. Add eight months. That is your real deadline, and it is probably earlier than you thought.
2. Ask the plan whether its drug coverage is creditable for Part D purposes, and keep the answer in writing.
3. Call your State Health Insurance Assistance Program. SHIP counsellors are free, government-funded, and cannot earn a commission on what you choose, which makes them structurally different from anyone who will call you after you fill in a quote form. Find yours through the national SHIP directory.
4. Compare properly. Get your COBRA number from the calculator or the election notice, then set it against Medigap or Medicare Advantage premiums for the same period rather than against nothing.
5. If you already think you have missed the window, still act now. The penalty is calculated per full 12-month period, so enrolling at the next opportunity limits the damage rather than leaving it to grow.

If you have already missed it

Enrollment is still possible during the General Enrollment Period, which runs annually in the first quarter of the year, with the penalty applied. In limited circumstances where the delay was caused by incorrect information from a federal employee or agent, Medicare has processes for equitable relief that can waive or reduce a penalty. It is not a formality and it is not guaranteed, but if you were actively told that COBRA counted as employment coverage, it is worth raising with Social Security and with a SHIP counsellor rather than assuming nothing can be done.