Medicare Part B Special Enrollment Period (SEP): Full Guide

What is the Part B Special Enrollment Period?

Most people sign up for Medicare during their Initial Enrollment Period (a 7-month window around their 65th birthday) or, if they miss that, during the General Enrollment Period (January 1 to March 31 each year, which can come with a lifelong late penalty).

A Special Enrollment Period (SEP) is a separate path that lets certain people enroll in Part B outside those windows without paying a penalty. The most common reason for a Part B SEP is having health coverage through an employer because you or your spouse were still working after 65.

• Initial Enrollment Period: the 7-month window centered on your 65th birthday month.
• General Enrollment Period: January 1 to March 31, often with a late penalty.
• Special Enrollment Period: a penalty-free path tied to a qualifying life event, such as losing job-based coverage.

Who qualifies, and how long is the window?

The most common Part B SEP applies if you (or your spouse) have group health plan coverage based on current employment. While that coverage is active, you can sign up for Part B anytime without a late penalty.

Once the active employment ends or the employment-based group coverage ends (whichever happens first), you get an 8-month Special Enrollment Period to sign up for Part B without a penalty.

If you keep working past 65 with this kind of coverage and do not want Part B yet, you generally do not have to sign up right away. But if you are about to retire, plan ahead so Medicare can start when your job coverage stops.

• Enroll anytime while you still have group coverage based on current employment, with no penalty.
• After that employment or coverage ends, you have an 8-month SEP to sign up for Part B penalty-free.

Why COBRA and retiree coverage are a trap

This is the single most common mistake people make. The 8-month SEP clock starts when your active employment (or the employment-based coverage) ends, even if you then pick up COBRA or another non-Medicare plan.

COBRA and retiree health plans are NOT considered coverage based on current employment. They do not extend your Part B SEP. You still have only 8 months from the time active employment ends, no matter how long your COBRA or retiree coverage lasts.

If you wait for COBRA to run out before signing up for Part B, you can blow past the 8-month window, end up with a gap in coverage, and face a lifelong late penalty.

• The SEP clock starts when you stop working, not when COBRA ends.
• COBRA and retiree coverage do not qualify as current-employment coverage.
• To avoid a gap, sign up for Part B the month before your (or your spouse's) job-based coverage ends so Medicare starts as the job coverage stops.

How to enroll and when coverage starts

To enroll using the employment-based SEP, you submit two forms to Social Security: Form CMS-40B (Application for Enrollment in Part B) and Form CMS-L564 (Request for Employment Information), which your employer or plan completes to confirm your coverage.

When you sign up for Part B during a Special Enrollment Period, coverage generally starts the first day of the month after Social Security (or the Railroad Retirement Board) receives your completed enrollment forms.

Keep in mind that joining a Medicare Advantage (Part C) or Part D drug plan after losing employer coverage has a much shorter SEP of only 2 months. Enrolling in Part D late can trigger a separate Part D late penalty, so handle drug coverage promptly even though you have 8 months for Part B.

• Forms needed: CMS-40B and CMS-L564, submitted to Social Security.
• Part B coverage usually starts the first day of the month after your forms are received.
• Part C / Part D SEP after employer coverage ends is only 2 months.

Exceptional-conditions SEPs (new since 2023)

Effective January 1, 2023, CMS created additional Part B Special Enrollment Periods for people who missed enrollment due to circumstances beyond their control. These come from a final rule under the Consolidated Appropriations Act, 2021.

• Disaster or emergency: if a government-declared emergency prevented timely enrollment, the SEP ends 6 months after the end date in the declaration.
• Misrepresentation: if an employer or health plan gave you incorrect information that caused you to miss enrollment, the SEP begins when you notify Social Security and ends 6 months later.
• Release from incarceration: the SEP starts at release and ends the last day of the 12th month after the month of release.
• Loss of Medicaid: if Medicaid eligibility is terminated on or after January 1, 2023, the SEP starts at notification and ends 6 months after the termination.
• Other exceptional conditions: CMS may grant a case-by-case SEP of no less than 6 months.
• For these SEPs, Part B coverage generally begins the first day of the month after you enroll (retroactive options may be available in some cases when premiums are paid).

The late penalty and 2026 Part B costs

Using a valid Part B SEP lets you avoid the Part B late enrollment penalty. That penalty otherwise adds 10% to your premium for each full 12-month period you were eligible for Part B but did not enroll, and you pay it for as long as you have Part B.

If you miss your SEP window, you generally have to wait for the General Enrollment Period (January 1 to March 31) to sign up, which can mean both a gap in coverage and the lifelong penalty.

For 2026, the standard Part B premium is $202.90 per month, with a $283 annual deductible. After you meet the deductible, you typically pay 20% coinsurance for most covered services. Higher-income enrollees may pay more through an income-related surcharge (IRMAA).

• Part B late penalty: 10% added per full 12 months you were eligible but not enrolled, for life.
• 2026 standard Part B premium: $202.90/month.
• 2026 Part B deductible: $283/year, then 20% coinsurance.
• Miss the SEP and you may have to wait until the General Enrollment Period (Jan 1 to Mar 31).