The small employer medicare mistake is one of the quietest financial traps in American health coverage. You turn 65. You are still working. Your group plan still deducts a premium from every paycheck. Nothing on your card changes. But if your employer has fewer than 20 employees, Medicare becomes your primary payer at 65, and your job’s plan drops to second in line. The small employer medicare mistake happens when nobody tells you that.
- The Rule Behind Small Employer Medicare Mistake
- Your Choices at 65
- The Penalty If You Get It Wrong
- Small Employer Medicare Mistake: the Paperwork
- The Traps People Fall Into
- Frequently Asked Questions
- Key Takeaways: Small Employer Medicare Mistake
- Compare Your Options
- Official Sources & Resources
- Related Guides
Claims get paid at a fraction of what you expected, or denied outright. Understanding the small employer medicare mistake before your 65th birthday is the difference between a routine enrollment and a lifetime penalty.
The Rule Behind Small Employer Medicare Mistake
Medicare Secondary Payer rules turn on one number: how many people your employer has. Twenty is the line.
If your employer has 20 or more employees, the group health plan generally pays first. Medicare pays second. You may delay Part B without penalty while that coverage continues, as described on Medicare.gov’s Working past 65 page.
If your employer has fewer than 20 employees, the order flips. Medicare pays first. Your job’s plan pays second. That reversal is where the small employer medicare mistake begins.
Here is the part that stings. Your small-employer plan may calculate its payment as if Medicare already paid its share. If you never enrolled in Part B, no Medicare payment exists. The secondary plan still pays only its secondary amount. You cover the gap yourself.
Some small employers join a CMS arrangement called the Small Employer Exception. Ask your benefits administrator in writing whether yours participates. Do not assume.
Your Choices at 65
You have three practical paths. Keep the job plan and add Medicare. Keep the job plan alone. Or drop the job plan and take Medicare with a supplement or Advantage plan.
Which path is safe depends entirely on employer size. The table below summarizes the payment order. Confirm your own employee count with your HR or benefits administrator before you decide.
| Employer size | Who pays first | What the reader should do |
|---|---|---|
| Fewer than 20 employees | Medicare pays first; the group plan pays second | Generally enroll in Part A and Part B at 65. Ask HR in writing how the plan pays if you do not have Part B. |
| 20 or more employees | The group health plan pays first; Medicare pays second | You may delay Part B while coverage from current employment continues. Keep written proof of every month of that coverage. |
| Multi-employer or union plan | Depends on plan rules and total employees | Request the plan’s coordination-of-benefits language in writing from the plan administrator. |
| COBRA or retiree coverage (any size) | Medicare pays first | This is not coverage based on current employment. Enroll in Part B on time. |
The small employer medicare mistake usually shows up in row one. People read “I have employer coverage” and stop reading there. Employer size, not the existence of a plan, controls the payment order.
Part A is premium-free for most people with enough work credits. Part B carries a monthly premium. Medicare.gov lists the standard Part B premium as $202.90 for 2026. Verify the current figure on Medicare.gov’s cost page, since higher-income enrollees pay more.
The Penalty If You Get It Wrong
The arithmetic is simple and unforgiving. Both penalties are described on Medicare’s Avoid late enrollment penalties page.
The Part B late enrollment penalty adds 10% to your monthly premium for each full 12-month period you could have had Part B but did not. Two full years late means a 20% surcharge. Four years late means 40%.
That surcharge is not a one-time fee. In most cases you pay it for as long as you have Part B. It is recalculated each year against the then-current standard premium, so it grows as premiums grow.
The Part D penalty works differently. It is 1% of the national base beneficiary premium, multiplied by the number of full months you went without creditable drug coverage. Medicare lists that base premium as $38.99 for 2026. The result is rounded to the nearest ten cents and added to your plan premium.
Twelve uncovered months would mean roughly $4.68 per month at the 2026 figure. Thirty-six months would be about triple that. You generally pay it for as long as you have Medicare drug coverage. See the Part D late enrollment penalty page and the CMS guidance on creditable coverage.
There is a timing penalty too. If you miss your window, you may have to wait for the General Enrollment Period, January 1 through March 31. Coverage then starts the first day of the month after you sign up.
Small Employer Medicare Mistake: the Paperwork
Two forms do the work. Knowing who signs each one prevents most delays.
Form CMS-40B, Application for Enrollment in Medicare Part B. You complete and sign this one yourself. It is the actual request to add Part B. The current form is posted at CMS.gov.
Form CMS-L564, Request for Employment Information. You fill in Section A. Your employer completes Section B, and an official company representative signs it, listing their title and phone number. The form is at CMS.gov.
❤️ Get Free Medicare Guides
Free · No spam · Unsubscribe anytime
Send both together to your local Social Security office. Find it through the SSA office locator. Keep a dated copy and proof of delivery.
Timing matters most. The Special Enrollment Period runs for 8 months after employment ends or the group coverage ends, whichever comes first. Medicare explains this on its enrollment timing page. Avoiding the small employer medicare mistake means starting the paperwork before that clock runs out, not after.
If a former employer will not complete Section B, ask Social Security what alternative proof it accepts. Pay stubs and W-2s are sometimes used. Confirm with SSA directly.
The Traps People Fall Into
COBRA is the most common one. COBRA is not coverage based on current employment. Your 8-month window starts when the job ends, not when COBRA ends. Medicare says this plainly on its COBRA page.
Retiree coverage carries the same problem. It does not protect you from the Part B penalty and does not create a Special Enrollment Period.
HSA contributions are the second trap. Once you are enrolled in Medicare, your HSA contribution limit is zero beginning that month. That rule is in IRS Publication 969.
Part A enrollment can be backdated when you apply after 65. Contributions made during a period of retroactive coverage become excess contributions, reported on Form 8889. Ask Social Security for your exact retroactive start date, then ask your tax preparer what to correct.
The last trap is the small employer medicare mistake itself: assuming your headcount is over 20 because the company feels busy. Count the employees. Get the answer in writing.
Frequently Asked Questions
How do I know if my employer has fewer than 20 employees?
Ask your benefits administrator or HR in writing. The count follows specific federal rules about employees on the payroll across calendar weeks. Ask them to state the answer and the basis for it. If they cannot, contact the Benefits Coordination and Recovery Center through CMS.
Can a late enrollment penalty ever be removed?
Medicare describes limited processes for review, including reconsideration of a Part D penalty determination. Whether any relief applies to your situation depends on your facts. Contact Social Security at 1-800-772-1213 and ask what request applies. This is a description of the process, not a prediction of any result.
Does my spouse’s small-employer plan change anything?
The same employer-size test applies to the employer providing the coverage. If your spouse works for an employer with fewer than 20 employees, the small employer medicare mistake risk is the same. Confirm the headcount with that employer.
I already made the small employer medicare mistake. What now?
Contact Social Security immediately to ask which enrollment period you qualify for and what forms to file. Ask your plan administrator, in writing, how it paid claims after your 65th birthday. Ask your tax preparer about any HSA contributions made after Medicare entitlement began.
Key Takeaways: Small Employer Medicare Mistake
- Employer size decides everything. Whether small employer medicare mistake 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 small employer medicare mistake lets them delay Part B.
Compare Your Options
Once you know what small employer medicare mistake 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.