Retiree coverage and medicare rarely pay in the order people expect. If you are still working at 65, or already past it, the order of payment depends on one fact: whether your health plan comes from current employment. That single detail decides whether you can safely delay Part B or must sign up now. Getting the order wrong can leave claims unpaid and add a premium surcharge you keep for life.
- The Rule Behind Retiree Coverage And Medicare
- Your Choices at 65
- The Penalty If You Get It Wrong
- Retiree Coverage And Medicare: the Paperwork
- The Traps People Fall Into
- Frequently Asked Questions
- Key Takeaways: Retiree Coverage And Medicare
- Compare Your Options
- Official Sources & Resources
- Related Guides
This guide walks through how retiree coverage and medicare interact under the Medicare Secondary Payer rules. It names the forms, the deadlines and the penalty math. It does not tell you which choice to make. Confirm your own employer’s size and plan status with your benefits administrator before you act, because only they can state it in writing.
The Rule Behind Retiree Coverage And Medicare
Medicare uses the Medicare Secondary Payer (MSP) rules to decide who pays first. The controlling factor is employer size and whether the coverage comes from active work. CMS explains the framework on its Medicare Secondary Payer page.
If the employer has 20 or more employees, the group health plan pays first. Medicare pays second. Both full-time and part-time employees count toward the 20. In a multi-employer plan, one participating employer with 20 or more employees can trigger the same result.
If the employer has fewer than 20 employees, Medicare generally pays first. The group plan pays second. That flip matters enormously. If you skipped Part B at a small employer, Medicare would have been primary — and the plan may deny the share Medicare would have covered.
Here is the part that surprises people. Retiree coverage and medicare do not follow the active-employment rule at all. Retiree coverage is not current employment coverage. Medicare pays first, and the retiree plan pays second, no matter how large the former employer is. Medicare’s Who pays first page states this directly.
So when retiree coverage and medicare overlap, the retiree plan is designed to wrap around Medicare, not replace it. Many such plans assume you enrolled in Part A and Part B on time. Read your plan document to see whether it reduces benefits once you are Medicare-eligible.
Your Choices at 65
Your Initial Enrollment Period runs seven months: three months before your 65th birthday month, the month itself, and three months after. If you keep coverage through current employment at a large employer, you may delay Part B and use a Special Enrollment Period later.
That Special Enrollment Period lasts eight months. It starts the month after employment ends or the group coverage ends, whichever comes first. Medicare describes the timing on its when coverage starts page.
| Your situation | Who pays first | What to do |
|---|---|---|
| Still working, employer has 20+ employees | Group health plan pays first; Medicare pays second | You may delay Part B. Keep proof of coverage for Form CMS-L564 later. |
| Still working, employer has fewer than 20 employees | Medicare pays first; group plan pays second | Ask the plan in writing whether it requires Part B. Most do. |
| Multi-employer plan, one employer has 20+ employees | Group health plan usually pays first | Confirm with the plan administrator, not the employer alone. |
| Retired, on former employer’s retiree plan | Medicare pays first; retiree plan pays second | Enroll in Part A and Part B on time. No Special Enrollment Period applies. |
| On COBRA after leaving a job | Medicare pays first; COBRA pays second | Do not rely on COBRA to delay Part B. The 8-month clock already started. |
| Spouse still working, employer has 20+ employees | Spouse’s group plan pays first | Delay is generally allowed. Confirm the employee count with that employer. |
Notice that the last three rows all describe non-current-employment situations. This is where retiree coverage and medicare create the most damage, because the coverage feels active but does not count as active for Medicare purposes.
The Penalty If You Get It Wrong
The Part B late enrollment penalty is 10 percent of the standard premium for each full 12-month period you could have had Part B but did not. It is added to your monthly premium for as long as you have Part B. Medicare sets out the rule on its avoid late enrollment penalties page.
Run the arithmetic. The standard Part B premium for 2026 is $202.90, per the CMS 2026 premiums fact sheet. A 24-month delay is a 20 percent penalty. That is roughly $40.58 added each month. The percentage does not expire, and it recalculates as the base premium rises.
Part D works differently. The penalty is 1 percent of the national base beneficiary premium for each full month you went without creditable drug coverage after a gap of 63 days or more. The 2026 national base beneficiary premium is $38.99. Medicare details the formula on its Part D late enrollment penalty page.
So 20 uncovered months equals 20 percent of $38.99, about $7.80 a month, rounded to the nearest ten cents. That amount is added to your drug plan premium for as long as you have Part D coverage. Ask your employer each year for the creditable coverage notice. It is your evidence.
Retiree Coverage And Medicare: the Paperwork
Two forms carry the weight. Form CMS-40B is the Application for Enrollment in Medicare Part B. You sign it yourself. Form CMS-L564 is the Request for Employment Information. You complete Section A; your employer or plan administrator completes and signs Section B.
Form CMS-L564 is what proves you had group health plan coverage based on current employment. Without it, Social Security cannot confirm your Special Enrollment Period. Where retiree coverage and medicare are involved, this form will not help, because retiree coverage is not current employment coverage.
Submit both forms to Social Security. You can file online, by fax or by mail through the Social Security Medicare sign-up portal. The deadline is the end of your eight-month Special Enrollment Period. If the employer will not sign Section B, ask Social Security what secondary evidence it will accept, such as pay stubs or W-2 forms.
Keep copies of everything. Note the date you filed. When retiree coverage and medicare are both in play, your retiree plan may also require a copy of your Medicare card before it will process claims as secondary.
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The Traps People Fall Into
COBRA is the most common trap. COBRA is not current employment coverage. Your Special Enrollment Period began when the job ended, not when COBRA ends. Many people discover this months after the eight-month window has closed.
The second trap is assuming a retiree plan substitutes for Part B. It does not. When retiree coverage and medicare overlap, the retiree plan pays second and often pays only what Medicare would have left. Skipping Part B can leave you responsible for the primary share yourself.
The third trap is the HSA. Once you enroll in any part of Medicare, your HSA contribution limit becomes zero for those months. Part A can be backdated up to six months, which turns earlier contributions into excess contributions. IRS Publication 969 explains the rule and the correction procedure.
The 2026 HSA limits are $4,400 for self-only and $8,750 for family coverage, set in Revenue Procedure 2025-19. If you plan to keep contributing past 65, stopping contributions at least six months before you file for Part A is the standard precaution. Confirm your own timing with a tax professional.
The fourth trap is the small employer. If your company has fewer than 20 employees, Medicare is primary even while you work. Delaying Part B there can create denied claims and a penalty at once. Ask the plan administrator to state the employee count in writing.
Frequently Asked Questions
Does retiree coverage let me delay Part B without a penalty?
No. Retiree coverage and medicare do not qualify you for a Special Enrollment Period, because retiree coverage is not based on current employment. Medicare pays first. Confirm your plan’s specific rules with the plan administrator before your Initial Enrollment Period ends.
Who signs Form CMS-L564?
You complete Section A. Your employer or group health plan administrator completes and signs Section B. You submit it to Social Security together with Form CMS-40B. If your employer refuses, contact Social Security and ask what alternative proof it will accept.
How long does the Part B penalty last?
For as long as you have Part B. It is 10 percent of the standard premium for each full 12-month period of delay. On the 2026 standard premium of $202.90, one full year of delay adds about $20.29 monthly.
Can I keep contributing to my HSA after 65 if I stay on my employer plan?
Only if you are not enrolled in any part of Medicare and remain on a qualifying high deductible plan. Enrollment in Part A alone ends eligibility. Because Part A can be backdated six months, review your timing with a tax professional first.
Key Takeaways: Retiree Coverage And Medicare
- Employer size decides everything. Whether retiree coverage and medicare is a choice or a requirement turns on the 20-employee rule.
- Part A is usually free. Most people take it at 65 even when retiree coverage and medicare lets them delay Part B.
- Except with an HSA. Part A ends HSA contributions, the one case where retiree coverage and medicare means delaying Part A too.
- COBRA does not count. For retiree coverage and medicare, COBRA is not active employer coverage, and assuming otherwise creates a lifetime penalty.
Compare Your Options
Once you know what retiree coverage and medicare means for you, the official Plan Finder shows what is actually sold in your ZIP code, and a SHIP counselor will walk it with you for free — no commission, no sales call.
Official Sources & Resources
- Social Security — Medicare enrollment: https://www.ssa.gov/medicare
- IRS Publication 969 (HSAs): https://www.irs.gov/publications/p969
- Medicare.gov: https://www.medicare.gov
- CMS.gov: https://www.cms.gov
- Find your SHIP counselor: https://www.medicare.gov/talk-to-someone
Checked against the official sources above in September 2026. Rules and dollar figures change; if a notice you received disagrees with this page, the notice wins — and please tell us. General information, not legal, financial or medical advice.