The Medicare Initial Enrollment Period is a 7-month window centered on a client's 65th birthday: 3 months before the birthday month, the birthday month itself, and 3 months after. Enrolling in Part B during the first 3 months gets the earliest possible effective date, which is the first of the birthday month. Every enrollment that happens in month 4 or later starts one month after the month of enrollment.
Key Takeaways
- The Medicare IEP is a 7-month window: 3 months before the birthday month, the birthday month itself, and 3 months after.
- Enrolling in Part B during the first 3 months of IEP means coverage starts the first day of the birthday month, the earliest possible effective date.
- Enrolling in Part B during the birthday month or any of the 3 months after it means coverage starts the first day of the month following enrollment.
- Clients already receiving Social Security before 65 are enrolled in Medicare Part A and Part B automatically; they must actively decline Part B in writing if they want to drop it.
- ACA Marketplace coverage does not satisfy the qualifying employer plan requirement that allows penalty-free delayed Medicare enrollment.
How the 7-month window is structured
The IEP is not an open-ended window. The clock starts running 3 calendar months before the month a client turns 65, and it closes 3 calendar months after that birthday month, regardless of whether the client has taken any action. A client born in October has an IEP that runs July through January. If they do nothing by January 31, the IEP closes.
Part A and Part B share the same 7-month IEP window. For most clients, premium-free Part A requires 40 or more quarters of Social Security-covered employment. Clients who do not meet the quarters threshold can still enroll in Part A during the IEP, but they pay a monthly premium based on their work history.
| IEP month | Enrollment timing relative to birthday | Part B coverage starts |
|---|---|---|
| Month 1 | 3 months before birthday month | 1st of birthday month |
| Month 2 | 2 months before birthday month | 1st of birthday month |
| Month 3 | 1 month before birthday month | 1st of birthday month |
| Month 4 | Birthday month | 1st of following month |
| Month 5 | 1 month after birthday month | 1st of following month |
| Month 6 | 2 months after birthday month | 1st of following month |
| Month 7 | 3 months after birthday month | 1st of following month |
Coverage start dates per 42 CFR 406.6(g) as updated effective January 2023. CMS eliminated the 2- and 3-month delays that previously applied to enrollments in IEP months 6 and 7. The maximum delay under current rules is one month.
The one case where enrollment is automatic
Clients who are already receiving Social Security retirement benefits or Railroad Retirement Board benefits before they turn 65 are enrolled in Medicare Part A and Part B automatically. CMS processes the enrollment, and the client receives their Medicare card by mail roughly 3 months before their birthday month. Coverage starts the first day of the birthday month.
The complication: automatic enrollment in Part B triggers the Part B premium from day one. Clients who have qualifying employer coverage at 65 and want to decline Part B to avoid paying the premium while still covered by an employer plan must contact SSA before coverage starts and request that Part B be dropped. They can re-enroll in Part B later using the Special Enrollment Period when employer coverage ends, without penalty, as long as that employer coverage was through current employment.
Clients who are not yet receiving Social Security at 65 must actively contact SSA or visit ssa.gov to enroll in Medicare. The enrollment does not happen automatically for them.
Part A timing and the first-of-birth-month rule
There is a specific rule for clients born on the first day of a month: their Medicare eligibility date is actually the first of the preceding month. A client born on July 1 becomes Medicare-eligible on June 1, not July 1. Their 7-month IEP runs March through September instead of April through October. Clients and brokers who calculate the IEP window from the birth date rather than the birth month can miss this one-month shift.
Example: a client born October 1 has a Medicare eligibility date of September 1. Their IEP runs June through December. If they enroll in Part B in October (which is month 5 of their IEP, not month 4), coverage starts November 1.
What happens when a client misses the IEP
A client who does not enroll in Part B during the IEP and does not have qualifying employer coverage must wait for the Medicare General Enrollment Period (GEP), which runs January 1 through March 31 each year. Coverage under the GEP starts July 1. That means a client who misses the IEP in, say, October can face up to 9 months without Part B coverage while they wait for the next GEP and then the July 1 start date.
On top of the coverage gap, every 12-month period without Part B after the IEP closes adds a 10 percent permanent late enrollment penalty to the Part B premium. A client who misses the IEP by 2 years pays a 20 percent penalty for life, calculated against whatever the standard premium is each year. In 2025, the standard Part B premium is $185.00 per month. A 2-year delay adds $37.00 per month, or $444 per year. The penalty does not expire.
The Medicare Part B late enrollment penalty guide for ACA brokers covers the penalty calculation and the limited circumstances under which SSA will waive it in detail.
Broker workflow for ACA clients approaching 65
ACA quoting tools, including platforms like Quotit, are built for Marketplace enrollment. None of them prompt the broker to check whether a client is approaching 65 or to verify their Medicare IEP window. That context has to come from the broker, not the software.
The practical workflow: at every ACA enrollment for a client who is 62 or older, confirm two things. First, will the client have qualifying employer-sponsored group health plan coverage through current employment at 65? If yes, they can delay Part B and use the 8-month SEP when that coverage ends. If no, they need to enroll in Part B during their IEP. Second, when does the IEP window open and close for this specific client? Do the math from the birth month, not the birthdate, and account for the first-of-month exception described above.
For clients in the 55-to-64 bracket navigating the years between employer coverage and Medicare eligibility, the ACA coverage guide for early retirees age 55 to 64 walks through the APTC landscape, Marketplace plan options, and the Medicare transition planning those clients need.
Medicare Initial Enrollment Period questions
IEP window mechanics, coverage start dates, automatic enrollment, and what ACA brokers need to explain to clients approaching 65.
What is the Medicare Initial Enrollment Period?
The Medicare Initial Enrollment Period (IEP) is the 7-month window during which a person turning 65 can enroll in Medicare Part A and Part B for the first time. The window opens 3 months before the month they turn 65, includes the birthday month, and runs 3 months afterward. Missing this window without qualifying employer coverage requires waiting for the General Enrollment Period (January 1 through March 31 each year, with coverage starting July 1) and incurring the Part B late enrollment penalty. The IEP is the only Medicare enrollment window with no prior authorization or triggering event required.
When does Part B coverage start if I enroll during the IEP?
The start date depends on which month of the 7-month window you enroll. If you enroll in one of the 3 months before your birthday month, Part B coverage starts the first day of your birthday month. If you enroll in your birthday month or in any of the 3 months after it, Part B coverage starts the first day of the month after you enroll. Effective January 2023, CMS simplified the old rule that imposed 2- and 3-month delays for late-window enrollments. Under the current rule, the maximum delay for any IEP enrollment is one month.
Does a client on an ACA Marketplace plan still need to enroll in Medicare at 65?
Yes. ACA Marketplace coverage is individual market insurance. It does not qualify as employer-sponsored group health plan coverage, which is the only coverage type that allows a client to delay Medicare Part B enrollment without penalty. A client who retires before 65, enrolls in a Marketplace plan, and then reaches 65 must enroll in Part B during their IEP or begin accruing the late enrollment penalty. The Marketplace plan covers them for medical services during the pre-Medicare years. It does not stop the penalty clock at 65 or create any delay right.
Is enrollment automatic if a client is already getting Social Security?
Yes. Clients who are already receiving Social Security retirement or disability benefits, or Railroad Retirement Board benefits, before they turn 65 are automatically enrolled in Medicare Part A and Part B. Their Medicare card arrives by mail approximately 3 months before the birthday month, and coverage starts the first of the birthday month. Clients who want to delay Part B because they still have qualifying employer coverage must actively contact SSA to decline it. Failing to decline and then dropping Part B to avoid the premium is possible but creates a gap that may trigger the penalty if the employer coverage is not still in place.
What should an ACA broker say to a 63-year-old client enrolling in a Marketplace plan?
The broker should confirm two things: whether the client will have employer-sponsored group health plan coverage through current employment at 65, and whether the client understands that they will need to enroll in Medicare during their IEP to avoid a permanent Part B cost. If the client will have qualifying employer coverage at 65, they can delay Part B and use the 8-month Special Enrollment Period when that coverage ends. If they will not, the IEP starts 3 months before their 65th birthday and closing enrollment in Part B later means either waiting for the General Enrollment Period or triggering the penalty. Quotit, Connecture, and similar ACA-focused platforms do not prompt for Medicare IEP status during enrollment, so the reminder has to come from the broker.
