COBRA and Medicare: How They Work Together (and the 8-Month Trap)

The core rule: COBRA does not delay Medicare

This is the single most expensive misunderstanding people make when leaving a job near age 65. COBRA lets you temporarily continue your former employer's health plan (typically up to 18 months) after your job ends. It feels like the same insurance you had while working — but Medicare treats it very differently.

Medicare only allows you to postpone Part B without penalty while you (or a spouse) are covered by a group health plan based on CURRENT employment. COBRA is not current employment — by definition it begins after your job has ended. Because of that, COBRA is generally not considered 'creditable' coverage for Part B and does not protect you from the Part B late-enrollment penalty.

The practical takeaway: if you are 65 or older and lose job-based coverage, treat Medicare — not COBRA — as your primary plan, and enroll in Part B on time even if you also elect COBRA.

The 8-month window — and why the clock starts early

When job-based coverage from current employment ends, you get a Special Enrollment Period (SEP) of 8 months to sign up for Part B without a late penalty. The critical detail that catches people off guard: that 8-month clock starts the month after your EMPLOYMENT (or the employer coverage) ends — not when your COBRA runs out.

Because COBRA can last 18 months but the Part B SEP is only 8 months, someone who relies on COBRA and waits until it ends can blow past the enrollment window entirely. At that point there is generally no Part B SEP available after COBRA ends, meaning you may have to wait for the General Enrollment Period and pay a permanent penalty.

• Part B late penalty: 10% added to your premium for each full 12-month period you could have had Part B but didn't — and it lasts for as long as you have Part B.
• If you delay because of COBRA rather than current employment, you typically will NOT qualify for a Part B SEP when COBRA ends.
• When in doubt, enroll in Part B during your Initial Enrollment Period (the 7 months around your 65th birthday) to avoid any risk.

Who pays first when you have both

If you have Medicare and COBRA at the same time, Medicare is almost always the primary payer and COBRA pays second. Because COBRA is secondary, it may cover only a small portion of your costs once Medicare has paid — so paying full COBRA premiums on top of Medicare often delivers limited extra value.

There is a narrow exception for End-Stage Renal Disease (ESRD): during the 30-month coordination period for ESRD, the group health plan (including COBRA) can pay first and Medicare pays second. Outside of that situation, expect Medicare to be primary.

• Medicare primary, COBRA secondary in most situations once you're Medicare-eligible.
• COBRA may pay little after Medicare pays — review whether the premium is worth it.
• ESRD is the main exception (30-month coordination period).

What happens to your COBRA once Medicare starts

Timing order matters. If you are already enrolled in Medicare BEFORE you elect COBRA, you are generally allowed to keep both — Medicare pays first and COBRA fills in as secondary for as long as you're eligible for it.

If you have COBRA FIRST and then become entitled to Medicare, your COBRA coverage will often end on the date your Medicare begins. In that case COBRA is not a safety net you can lean on — which is exactly why enrolling in Part B on time is so important.

A spouse or dependents on your COBRA plan may be able to continue their COBRA even after your coverage ends, but the rules depend on the specific plan and situation. Confirm details with the plan administrator before making assumptions.

Don't forget Part D prescription drug coverage

Medicare's prescription drug rules are separate from Part B. When your COBRA coverage ends, you generally get a 2-month Special Enrollment Period to join a Medicare Part D drug plan or a Medicare Advantage plan with drug coverage. This Part D SEP is narrower than the Part B timeline, so don't conflate the two.

Whether you owe a Part D late penalty depends on whether your drug coverage was 'creditable' (at least as good as standard Medicare drug coverage). Some COBRA plans offer creditable drug coverage and some do not — ask your plan for its annual creditable-coverage notice in writing.

The Part D late-enrollment penalty is calculated as 1% of the national base beneficiary premium ($38.99 in 2026) times the number of full months you went without creditable drug coverage, and it is generally added to your premium for as long as you have Part D.

2026 Medicare costs to plan around

If you move from COBRA to Medicare, here is what standard 2026 Medicare costs look like, so you can compare against your COBRA premium. Most people pay no premium for Part A because they have 40+ quarters of Medicare-covered work.

• Part B: $202.90/month standard premium; $283 annual deductible; you pay 20% coinsurance for most services after the deductible.
• Part A: premium-free with 40+ work quarters ($311/month at 30–39 quarters; $565/month with under 30 quarters); $1,736 deductible per benefit period.
• Part D: out-of-pocket spending is capped at $2,100 for the year in 2026; the national base premium is $38.99/month.
• Higher earners may pay IRMAA surcharges on Part B and Part D when income (2024 MAGI) exceeds $109,000 single / $218,000 joint.