Yes, you can have Medicare Part B and employer coverage at the same time. Millions of Americans do it every year. The real question is not whether you can hold both — it is how they work together and which one pays your medical bills first.
Under 42 U.S.C. § 1395y, a federal law called the Medicare Secondary Payer (MSP) statute controls this entire process. This law decides whether Medicare or your employer plan acts as the primary payer — the one that pays first. Getting this wrong can leave you stuck with thousands of dollars in uncovered medical bills and permanent premium penalties.
About 8% of all Medicare Part B enrollees pay higher premiums due to income-related adjustments, and many others face late enrollment penalties they could have avoided with the right timing. The standard Part B premium for 2026 is $202.90 per month, with an annual deductible of $283.
Here is what you will learn:
- 🏥 How Medicare Part B and employer coverage coordinate — and which one pays first based on your employer’s size
- ⚖️ The exact federal rules under the Medicare Secondary Payer statute that control your coverage
- 💰 When you must enroll in Part B to avoid a lifetime late enrollment penalty
- 📋 How to fill out the CMS-L564 and CMS-40B forms step by step during the Special Enrollment Period
- 🚫 The most common mistakes people make — including the COBRA trap that catches thousands off guard
How the Medicare Secondary Payer Rule Controls Everything
The Medicare Secondary Payer (MSP) rule is the backbone of how Medicare Part B and employer coverage interact. It was created to stop Medicare from paying bills that a private employer plan should cover first. The Benefits Coordination & Recovery Center (BCRC) at CMS manages this entire process.
The primary payer pays up to its coverage limits first. The remaining balance then goes to the secondary payer. If the secondary payer does not cover what is left, you pay the rest out of pocket. This order of payment is called coordination of benefits.
The MSP rule prevents employers from taking into account the Medicare entitlement of a current employee or their spouse. This means a large employer cannot pressure you into dropping the group plan just because you turned 65. It also cannot offer you a lesser health plan because of your Medicare eligibility.
Your Employer’s Size Is the Single Biggest Factor
The number of employees at your company determines which plan pays first. The rule is straightforward, but the consequences of ignoring it are severe.
| Employer Size | Who Pays First (Primary) | Who Pays Second (Secondary) |
|---|---|---|
| 20 or more employees (age 65+) | Employer group health plan | Medicare |
| Fewer than 20 employees (age 65+) | Medicare | Employer group health plan |
| 100 or more employees (under 65, disability) | Employer group health plan | Medicare |
| Fewer than 100 employees (under 65, disability) | Medicare | Employer group health plan |
The MSP employer size requirement counts all employees — full-time and part-time — for each working day in at least 20 calendar weeks in the current or preceding calendar year. Each part-time employee counts as one full employee. Employees who do not participate in the group health plan are still included in the headcount. Self-employed individuals participating in the plan are not counted.
If an employer reaches the 20-employee threshold during the current year, the MSP rules kick in immediately and remain in effect through the end of the following calendar year. Even if the headcount drops below 20 after meeting the threshold, the employer stays subject to the MSP rules through at least the remainder of that calendar year.
When Your Employer Has 20 or More Employees
If you are 65 or older and work for a company with 20 or more employees, your employer’s group health plan is the primary payer. Medicare Part B becomes the secondary payer. This is where most working Americans over 65 find themselves.
You have a choice here. You can enroll in Part B alongside your employer coverage, or you can delay Part B enrollment without penalty. Because the employer plan pays first, Medicare is not essential for covering your medical costs while you are still working and covered.
Why Some People Enroll in Both Anyway
Carrying both plans gives you a safety net. Your employer plan pays first, and then Medicare picks up much of what is left — including copays, coinsurance, and deductible costs your employer plan did not fully cover. Together, the two plans often cover close to 100% of your total claim so you pay little or nothing out of pocket.
Why Some People Delay Part B
The standard Part B premium is $202.90 per month in 2026. If your employer plan provides strong coverage and you do not want to pay that extra premium, you can delay Part B without any penalty as long as you remain covered under a group health plan based on current employment. You or your spouse must be actively working — this is a critical detail.
When Your Employer Has Fewer Than 20 Employees
This is where the rules flip, and the consequences get serious. If you are 65 or older and your employer has fewer than 20 employees, Medicare becomes the primary payer. Your employer plan drops to secondary.
You must enroll in Medicare Part B at age 65 in this situation. If you do not, Medicare will not pay your claims because you are not enrolled. Your employer plan will not pay first because federal law says it is secondary. The result? You could be responsible for 100% of your medical bills.
Some employer plans for small companies will still cover claims even if you do not have Part B. But this is rare and unreliable. Never assume your small employer’s plan will act as primary — it is required by law to pay second.
The HSA Trap for Small Employer Workers
If you have a Health Savings Account (HSA) tied to a high-deductible health plan at a small employer, enrolling in Medicare Part B means you must stop contributing to your HSA. Federal tax rules prohibit HSA contributions once you are enrolled in any part of Medicare. Your spouse can still contribute to the HSA if they are covered on your group plan and are not enrolled in Medicare themselves.
Scenario 1: Linda Works at a Large Company and Turns 65
Linda is a 65-year-old marketing director at a company with 150 employees. She has excellent group health insurance through her employer. She wants to know if she should sign up for Part B.
Because her employer has more than 20 employees, her employer plan is primary and Medicare is secondary. Linda decides to enroll in Part B anyway because she wants the extra layer of coverage.
| What Linda Does | What Happens |
|---|---|
| Enrolls in Part B at 65 while still working | Employer plan pays first, Medicare Part B pays second — very low out-of-pocket costs |
| Delays Part B until she retires | No penalty — she qualifies for a Special Enrollment Period when employment ends |
| Visits a specialist with a $5,000 bill | Employer plan covers its share first, Medicare Part B covers most of the remaining balance |
| Retires at age 68 | She has 8 months to enroll in Part B penalty-free using the SEP |
Linda pays $202.90 per month for Part B in 2026, but she rarely pays anything at the doctor because her two plans together cover almost all her costs.
Scenario 2: Robert Works at a Small Business and Turns 65
Robert is a 65-year-old mechanic at an auto shop with 12 employees. He has group health insurance through his employer. Robert assumes his employer plan will keep covering him the same way it always has.
Because his employer has fewer than 20 employees, Medicare is primary. Robert’s employer plan is secondary. Robert must enroll in Part B at 65.
| What Robert Does | What Happens |
|---|---|
| Enrolls in Part B at 65 as required | Medicare pays first, employer plan covers remaining costs — Robert is fully protected |
| Skips Part B thinking his employer plan is enough | Employer plan refuses to pay as primary — Robert is stuck with major medical bills |
| Waits until age 67 to enroll in Part B | Faces a 20% lifetime penalty added to his monthly Part B premium |
| Has an HSA and enrolls in Part B | Must stop HSA contributions immediately |
Robert’s two-year delay costs him an extra $40.58 per month on top of his $202.90 premium — for the rest of his life. That adds up to over $487 per year in penalty charges that never go away.
Scenario 3: Patricia Retires and Relies on COBRA
Patricia is 66 years old. She just retired from a large company and elected COBRA coverage to bridge the gap. She assumes COBRA will protect her from Part B penalties because it is technically continued employer coverage.
Patricia is wrong. COBRA is not considered coverage based on current employment for Medicare purposes. The 8-month Special Enrollment Period clock started the day her active employment ended — not when COBRA runs out.
| What Patricia Does | What Happens |
|---|---|
| Elects COBRA and delays Part B for 18 months | Her 8-month SEP window closes — she now faces a late enrollment penalty |
| Relies on COBRA as primary coverage after 65 | COBRA may reduce or deny benefits because Medicare should be primary |
| Misses the 8-month SEP window | Must wait until General Enrollment (January–March) for coverage starting July 1 |
| Enrolls during General Enrollment after a 12-month gap | Pays a 10% lifetime penalty on her Part B premium |
COBRA-qualified beneficiaries who delay Part B do not qualify for a Special Enrollment Period once COBRA ends. Patricia faces both a coverage gap and a permanent surcharge because she misunderstood the rules.
The Part B Late Enrollment Penalty Explained
The Part B late enrollment penalty is one of Medicare’s harshest consequences. It adds 10% to your monthly premium for every full 12-month period you were eligible but did not enroll — and you pay this penalty for as long as you have Part B.
The 2026 standard Part B premium is $202.90 per month. The annual deductible is $283. Penalties stack on top of these amounts.
| Years Without Part B (No Qualifying Coverage) | Penalty Percentage | Monthly Premium in 2026 (with penalty) |
|---|---|---|
| 1 year | 10% | $223.19 |
| 2 years | 20% | $243.48 |
| 3 years | 30% | $263.77 |
| 5 years | 50% | $304.35 |
These penalties are permanent. They are recalculated each year as the base premium changes, meaning the dollar amount of your penalty grows over time even though the percentage stays the same.
How to Avoid the Penalty
You avoid the penalty by enrolling in Part B during one of these windows:
- Initial Enrollment Period (IEP): A 7-month window around your 65th birthday (3 months before, your birthday month, and 3 months after)
- Special Enrollment Period (SEP): Available while you or your spouse are actively working and covered by a group health plan, plus 8 months after that employment or coverage ends
- General Enrollment Period (GEP): January 1 through March 31 each year, with coverage starting July 1 — but this route usually comes with the penalty
The SEP is the most important protection for working Americans over 65. It allows you to delay Part B without penalty as long as you have qualifying coverage through current employment.
The 8-Month Special Enrollment Period Window
Once your employment ends or your group health plan coverage ends (whichever happens first), you have exactly 8 months to enroll in Part B without a penalty. This 8-month clock is strict, and it does not pause or reset.
The 8-month period begins the month after your employment ends — not the month after your COBRA coverage ends. COBRA does not extend this window. Retiree coverage does not extend it either. Only coverage through active, current employment counts.
If you miss this 8-month window, you must wait for the next General Enrollment Period (January 1–March 31), and your coverage will not begin until July 1 of that year. That gap can leave you exposed to large medical bills for months.
How to Enroll: The CMS-L564 and CMS-40B Forms
Two forms are required when enrolling in Part B during a Special Enrollment Period. Both are submitted to your local Social Security office.
Form CMS-L564: Request for Employment Information
The CMS-L564 is the form your employer fills out. It proves to Social Security that you had group health plan coverage based on current employment. This is the evidence that qualifies you for the SEP and protects you from the late enrollment penalty.
What your employer provides on this form:
- The company name, address, and phone number
- Whether the group health plan coverage was based on your current employment status
- The dates your group health plan coverage began and ended
- Whether you are still employed or the date your employment ended
Your employer’s HR or benefits department completes this form. It must be accurate because Social Security uses it to verify your eligibility for a penalty-free enrollment. Errors or missing information can delay your enrollment.
Form CMS-40B: Application for Enrollment in Medicare Part B
The CMS-40B is the form you fill out. It is your official application to enroll in Part B.
What you provide on this form:
- Your Medicare number (found on your red, white, and blue Medicare card)
- Your full name, current address, and phone number
- Your date of birth and Social Security number
- The reason you are applying for Part B after your Initial Enrollment Period
- Your current employment status
You submit both forms together — the completed CMS-L564 from your employer and the completed CMS-40B from you — to your local Social Security office. You can also mail them or, in some cases, submit them online. If you have questions during the process, call Social Security at 1-800-772-1213 (TTY: 1-800-325-0778).
Mistakes to Avoid That Cost People Thousands
Mistake 1: Assuming COBRA Delays Part B Without Penalty
COBRA continues your employer group health plan coverage, but it is not considered coverage based on current employment. The 8-month SEP clock starts when your active employment ends, not when COBRA ends. People who wait for COBRA to expire before enrolling in Part B lose their SEP entirely and face lifetime penalties.
Mistake 2: Not Enrolling in Part B at a Small Employer
Workers at companies with fewer than 20 employees must enroll in Part B at 65. Medicare is primary in this situation. Skipping Part B means neither plan pays first, leaving you responsible for the full cost of care.
Mistake 3: Thinking Retiree Coverage Counts for the SEP
Retiree health coverage is not the same as coverage through current employment. If you retire and move to a retiree plan, your 8-month SEP window has already started. Retiree coverage does not qualify you for a Special Enrollment Period.
Mistake 4: Forgetting to Submit the CMS-L564 Form
If you apply for Part B during the SEP but forget to include the CMS-L564 form from your employer, Social Security may not be able to verify your eligibility. This can result in delays or an incorrect penalty being applied to your account.
Mistake 5: Contributing to an HSA After Enrolling in Medicare
Once you enroll in any part of Medicare — including Part A — you cannot contribute to a Health Savings Account. Excess contributions trigger a 6% tax penalty each year they remain in the account. Plan your last HSA contribution carefully around your Medicare enrollment date.
Pros and Cons of Holding Both Medicare Part B and Employer Coverage
| Pros | Cons |
|---|---|
| Very low out-of-pocket costs — two plans cover nearly 100% of claims | Extra monthly cost — Part B premium of $202.90/month in 2026 on top of any employer plan premiums |
| No coverage gaps — if one plan denies a claim, the other may cover it | Coordination headaches — providers must bill the correct payer first, and errors cause claim denials |
| No late enrollment penalty — enrolling on time protects you permanently | HSA contributions must stop — you cannot fund an HSA while enrolled in any part of Medicare |
| Broader provider network — Medicare is accepted nearly everywhere in the U.S. | Potential for duplicate coverage — you may pay for benefits you do not need |
| Protection at retirement — Part B is already active when you leave your job, so there is no gap in coverage | Income-based surcharges — high earners pay significantly more for Part B through IRMAA adjustments |
Do’s and Don’ts for Coordinating Coverage
Do’s
- Do check your employer’s size — the 20-employee threshold is the single most important factor in deciding who pays first and whether you must enroll in Part B at 65
- Do enroll in Part B at 65 if your employer has fewer than 20 employees — Medicare is primary, and skipping Part B leaves you uncovered
- Do keep the CMS-L564 form on file — ask your employer to complete it before you retire so you have it ready when you need it
- Do contact the BCRC at 1-855-798-2627 if you are unsure who pays first — this is the federal office that handles coordination of benefits
- Do report any insurance changes to both Medicare and your employer plan to prevent billing errors and claim denials
Don’ts
- Don’t assume COBRA extends your SEP — COBRA is not current employment coverage, and the 8-month clock starts when your job ends
- Don’t skip Part B at a small employer — you risk paying 100% of your medical bills because your employer plan is legally secondary
- Don’t contribute to an HSA after enrolling in Medicare — it triggers a 6% IRS penalty on excess contributions each year
- Don’t wait for General Enrollment if you have an SEP available — General Enrollment coverage does not start until July 1, creating a potentially dangerous gap
- Don’t ignore income-related Part B surcharges — if your modified adjusted gross income exceeds $109,000 (individual) or $218,000 (joint), you pay a higher premium called IRMAA
Section 105 Medical Reimbursement Plans for Small Employers
Small employers who cannot offer traditional group health plans have another option. A Section 105 Medical Reimbursement Plan allows employers to set aside tax-free funds for workers to use toward health insurance, including Medicare Part B premiums.
This is a powerful tool for small business employees over 65 who must enroll in Part B because Medicare is their primary payer. The employer reimburses the employee’s Part B premium tax-free, reducing the financial burden of mandatory enrollment. Section 105 plans can also cover dental insurance and other medical expenses.
How Income Affects Your Part B Premium (IRMAA)
Medicare uses your modified adjusted gross income (MAGI) from two years ago to determine if you owe extra. This surcharge is called the Income-Related Monthly Adjustment Amount (IRMAA). It is added on top of the standard Part B premium.
| Individual Income (2024 Tax Return) | Joint Income (2024 Tax Return) | 2026 Monthly Part B Premium |
|---|---|---|
| $109,000 or less | $218,000 or less | $202.90 |
| $109,001–$137,000 | $218,001–$274,000 | $284.10 |
| $137,001–$171,000 | $274,001–$342,000 | $365.30 |
| $171,001–$205,000 | $342,001–$410,000 | $446.50 |
| $205,001–$499,999 | $410,001–$749,999 | $527.70 |
| $500,000 or more | $750,000 or more | $578.30 |
These IRMAA brackets are set by CMS each year. About 8% of Part B enrollees pay the higher amount. If your income has dropped significantly since the tax year used for the calculation — for example, because you retired — you can file an appeal with Social Security using Form SSA-44.
FAQs
Can I delay Medicare Part B if I have employer coverage?
Yes. You can delay Part B penalty-free if you have group health plan coverage through current employment at an employer with 20 or more employees.
Does COBRA count as employer coverage for delaying Part B?
No. COBRA is not considered coverage through current employment. The 8-month Special Enrollment Period starts when active employment ends, not when COBRA expires.
Will I pay a penalty if I enroll in Part B late?
Yes, unless you qualify for a Special Enrollment Period. The penalty is 10% of the premium for each full 12-month period you were eligible but not enrolled.
Can my spouse’s employer coverage delay my Part B enrollment?
Yes. If your spouse is actively working and you are covered under their employer group health plan with 20 or more employees, you qualify for the SEP.
What happens if my employer has exactly 20 employees?
Yes, the MSP rules apply. An employer with 20 or more employees must offer primary coverage to employees and spouses aged 65 and older.
Do I need Part B if I have VA health care?
No, Part B is not required to receive VA care. However, VA coverage does not count as employer group health plan coverage for SEP purposes.
Can my employer force me to drop their plan and use Medicare?
No. Under the MSP statute, employers with 20 or more employees cannot take into account your Medicare eligibility when offering group health plan benefits.
Is the Part B late enrollment penalty permanent?
Yes. The penalty applies for as long as you have Part B. It is recalculated annually as the base premium changes, so the dollar amount increases over time.
When does Part B coverage start if I use the General Enrollment Period?
No, coverage does not start right away. If you enroll during the GEP (January 1–March 31), your Part B coverage begins July 1 of that year.
Do I need both Part A and Part B at a small employer?
Yes. At an employer with fewer than 20 employees, Medicare is primary. You need both Part A and Part B at age 65 to avoid coverage gaps and penalties.
Related reading
- Can You Have Medicare Part B Without Part A? (w/Examples) + FAQs
- Can You Have Medicare Part B and Private Insurance? (w/Examples) + FAQs
- Can Medicare Part B Be Secondary Insurance? (w/Examples) + FAQs
- Are Medicare Part B Premiums Paid in Advance? (w/Examples) + FAQs
- Can Medicare Part B Premiums Be Paid From HSA? (w/Examples) + FAQs
- Is Medicare Part B Deducted From Social Security? (w/Examples) + FAQs
- Is Nationwide Long-Term Care Insurance Worth It? (w/Examples) + FAQs