The Medicare Part B late enrollment penalty adds 10 percent to the standard monthly premium for every 12-month period a beneficiary delayed enrollment past their initial window. In 2025, that is $18.50 per month per uncovered year. A client who delayed three years owes an extra $55.50 per month. The penalty does not expire; it runs for the rest of the beneficiary's Medicare lifetime. For a client on a fixed income, this is not a footnote.
ACA-focused platforms, including newer enrollment tools in the Inshura category built around Marketplace workflow, are not designed to flag this. They are enrollment tools, not Medicare transition planners. The prompt to have this conversation with a 63-year-old enrolling in a Marketplace plan does not appear in the quoting software. It has to come from the broker.
Key Takeaways
- ACA Marketplace plans do not delay or satisfy the Medicare Part B enrollment requirement.
- The 8-month SEP for Part B begins when qualifying employer coverage ends, not at age 65.
- The Part B LEP is 10 percent per uncovered 12-month period, compounding, and permanent.
- A 3-year delay beyond the SEP window adds 30 percent to the Part B premium for life.
- Every ACA enrollment for a client approaching 65 should include a Medicare timing conversation.
Why Marketplace plans do not help with the Part B penalty
Medicare Part B has its own enrollment rules, and those rules recognize only one category of coverage as a reason to defer Part B without penalty: employer-sponsored group health plan coverage through current employment. A client who is 65, working, and covered on an employer plan does not need to enroll in Part B until the employment or coverage ends. When it does, the 8-month special enrollment period begins.
An ACA Marketplace plan is individual market coverage, not employer-sponsored coverage. Enrolling in a Marketplace plan at 65 instead of Medicare does not pause the penalty clock. The client is accruing penalty months from the day their initial enrollment period or SEP closes, regardless of whether they have Marketplace coverage. They are not uninsured in the conventional sense during those months, but they are accumulating a Medicare cost that will follow them permanently.
The 8-month SEP: how it starts and why it matters
When a client retires or loses employer-sponsored group health plan coverage, the 8-month SEP is the window for penalty-free Part B enrollment. CMS regulations set the start date at the first day of the month after employment ends or coverage ends, whichever occurs first.
The common misunderstanding is that the SEP starts at age 65. It does not. A client who worked past 65 and had employer coverage does not need to use their Initial Enrollment Period (the 7-month window around the 65th birthday). They can delay Part B through the employment period and rely on the SEP when coverage ends. But a client who stopped working at 63, enrolled in a Marketplace plan, and turns 65 without employer coverage must use the Initial Enrollment Period at 65. If they miss it, the SEP does not apply because the SEP is triggered by loss of qualifying employer coverage, which already ended two years ago.
| Client situation | Coverage at 65 | Part B enrollment window | Penalty risk |
|---|---|---|---|
| Working, employer plan | Employer group health plan | 8-month SEP after coverage ends | None if SEP used |
| Retired before 65, on ACA plan | Marketplace plan (not qualifying) | Initial Enrollment Period at 65 (7-month window) | LEP if IEP missed |
| Retired at 65, skipped Part B | Marketplace plan or nothing | GEP (Jan 1–Mar 31); July coverage | LEP for each full uncovered year |
| On spouse's employer plan at 65 | Spouse's group health plan (qualifying) | 8-month SEP after spouse's coverage ends | None if SEP used |
Illustrative scenarios. Actual Medicare eligibility rules depend on individual circumstances. Confirm enrollment timing with SSA or a Medicare-licensed advisor.
The penalty math: what delayed enrollment actually costs
The penalty calculation uses the standard Part B premium as the base, even if the client pays more due to IRMAA. CMS adjusts the standard premium annually, so the dollar amount of the penalty changes each year while the percentage stays fixed.
Example: a client who retired at 63, enrolled in a Marketplace plan, turned 65 in 2022, and missed the Initial Enrollment Period accrues 12 months in 2022, 12 months in 2023, and enrolls during the 2024 General Enrollment Period. That is a 30 percent penalty, calculated against whatever the standard premium is at enrollment and each year after. At a $185 monthly standard premium, the annual penalty cost is $666. Over 20 years of Medicare coverage, the compounded dollar cost of that missed enrollment window is substantial.
The penalty does not disappear if the client later establishes employer coverage. Once accrued, it applies for life.
What to say at an ACA enrollment for a client approaching 65
For clients enrolling in a Marketplace plan who are between 62 and 64, the broker should confirm two things before closing the enrollment: whether the client has or will have employer-sponsored coverage at 65, and whether the client understands that the Marketplace plan will need to be replaced by Medicare at 65 to avoid a permanent Part B cost.
The exact framing depends on the situation. A 63-year-old who retired from a job with no retiree coverage needs to know that their Marketplace plan is a bridge to Medicare, and that the bridge ends at the Initial Enrollment Period. A 63-year-old still working part-time with employer coverage needs a different conversation about whether that coverage qualifies and when it will end.
Neither conversation is complicated. Both conversations take two minutes. Skipping them because the broker's platform does not prompt for Medicare status is the exact scenario that generates a $55 per month penalty for someone on Social Security income.
Medicare Part B enrollment questions for ACA brokers
Late enrollment penalties, SEP windows, Marketplace creditable coverage, and what to say to clients approaching 65.
Does an ACA Marketplace plan count as creditable coverage for Medicare Part B purposes?
No. ACA Marketplace plans are not qualifying coverage for the purpose of avoiding the Medicare Part B late enrollment penalty. The Medicare late enrollment rules recognize employer-sponsored group health plan coverage tied to current employment as the coverage type that defers the Part B enrollment requirement. A client who leaves an employer at 65 and enrolls in a Marketplace plan instead of Medicare Part B is accumulating the penalty from the moment their 8-month special enrollment period expires. The Marketplace plan covers them for medical services, but it does not stop the LEP clock.
How does the Medicare Part B 8-month special enrollment period work?
When a client who is 65 or older loses employer-sponsored group health plan coverage (either through their own employment or a spouse's), they have 8 months to enroll in Medicare Part B without a penalty. The window opens on the first day of the month after employer coverage ends, or employment ends, whichever comes first. The 8-month SEP does not extend because the client enrolls in a Marketplace plan. A client who misses the 8-month window must wait for the Medicare General Enrollment Period (January 1 through March 31 each year) with July 1 coverage, plus the late enrollment penalty on top of the standard premium.
How is the Medicare Part B late enrollment penalty calculated?
The penalty is 10 percent of the standard Part B monthly premium for each full 12-month period the client went without Part B coverage after their initial enrollment period or SEP ended. In 2025, the standard Part B premium is $185.00 per month. A client who delayed 24 months would pay a 20 percent penalty, or $37.00 per month on top of the standard premium, for a total of $222.00 per month. Because the penalty is calculated against the standard premium, which CMS adjusts annually, the dollar amount of the penalty changes each year, but the percentage does not. The percentage is permanent.
What should an ACA broker say to a client who is 62 and enrolling in a Marketplace plan?
The broker should confirm whether the client will have employer-sponsored coverage through employment at any point before age 65, and note that if they do not, they will need to enroll in Medicare Part B during their Initial Enrollment Period (the 7-month window around their 65th birthday) to avoid the penalty. If the client will have employer coverage at 65, they can delay Part B and use the 8-month SEP after that coverage ends. The Marketplace plan is appropriate for the years before 65; it does not interact with Medicare timing one way or another until the client reaches Medicare eligibility.
Can a client appeal or get the Medicare Part B late enrollment penalty waived?
CMS does not have a general waiver process for the Part B late enrollment penalty. Exceptions are narrow: CMS can remove the penalty if the client had coverage that was incorrectly reported as non-qualifying, or in cases where CMS or SSA administrative error caused the delay. A client who was misled by a broker, an insurer, or an employer into believing their non-qualifying coverage protected them may have grounds to request an exception, but CMS adjudicates these individually and approval is not guaranteed. The practical advice for brokers is that prevention is the only reliable solution.
