Is Medicare Part B Mandatory in 2026? (Late Enrollment Penalty)

Direct Answer: Is Part B Mandatory?

No. Medicare Part B is voluntary in 2026. You can legally decline or delay enrollment. However, delaying without a valid Special Enrollment Period triggers a permanent late enrollment penalty: an additional 10% of the standard 2026 premium ($202.90/month) for each full 12-month period you went without Part B coverage. Miss two full years and your premium surcharge is 20% forever. The only penalty-free delay is through the employer group health plan Special Enrollment Period.

When You Are Automatically Enrolled in Part B

Medicare automatically enrolls you in both Part A and Part B if you are already receiving Social Security or Railroad Retirement Board (RRB) benefits at least 4 months before your Medicare eligibility date. Your red, white, and blue Medicare card arrives in the mail roughly 3 months before your 65th birthday. Part B coverage begins on the first day of the month you turn 65 (or the first day of the month you turn 65 if your birthday is on the first, it starts the month before).

Auto-enrollment is not irrevocable. You can refuse Part B by returning the Medicare card with the Part B opt-out section completed, but doing so is permanent for that enrollment window. If you later want Part B, you will face the late enrollment penalty unless you qualify for an SEP. Puerto Rico residents who are auto-enrolled receive Part A only; they must separately and actively apply for Part B.

The Late Enrollment Penalty: How It Is Calculated in 2026

The Part B late enrollment penalty adds 10% to the standard monthly premium for each full 12-month period you were eligible but not enrolled. Partial years do not count. The penalty applies to the current year's standard premium, which means it adjusts upward each year as the standard premium changes. In 2026 the standard premium is $202.90/month, so each year of delay adds $20.29/month ($202.90 x 10%) to your premium.

The Employer Group Health Plan Exception: When Delaying Part B Is Safe

Medicare Part B can be safely delayed without penalty if you are actively working and covered by a group health plan from your own current employer (or your spouse's current employer) where the company has 20 or more employees. Both conditions must be true simultaneously: the job must be active (not retired), and the employer must have 20 or more employees. Under this rule, the employer plan pays first and Medicare pays second (secondary payer rules), so you can defer Part B while your employer plan handles most claims.

When active employment ends or the group coverage terminates (whichever happens first), an 8-month Special Enrollment Period begins. You must enroll in Part B within those 8 months to avoid the late enrollment penalty. Common mistake: many people confuse COBRA with active employer coverage. COBRA is continuation coverage after employment ends and does not qualify for the SEP exception. Retiree health plans and marketplace individual plans also do not count. Waiting beyond the 8-month SEP window means you must wait for the General Enrollment Period (January 1 to March 31) with coverage starting the following month, plus the full penalty applies.

Enrollment Windows for Part B in 2026

Original Medicare Part B offers three enrollment windows in 2026. The Initial Enrollment Period (IEP) is the 7-month window centered on your 65th birthday: it opens 3 months before the month you turn 65, includes your birthday month, and closes 3 months after. Enrolling in the first 3 months of the IEP means Part B starts on the first day of your birthday month. Enrolling in your birthday month or later means coverage starts 1 to 3 months after signup.

The Special Enrollment Period (SEP) for employer coverage runs for 8 months after employment or group coverage ends. Coverage starts the first day of the month after you enroll. The General Enrollment Period (GEP) is January 1 through March 31 each year, available for anyone who missed the IEP and does not qualify for an SEP. A 2023 rule change means GEP coverage now starts on the first of the month after you enroll (no more waiting until July). The late enrollment penalty still applies during GEP enrollment if you missed your IEP or SEP.

Medicare Part B and Medicare Advantage in 2026

Medicare Advantage (Part C) plans are private plans that replace Original Medicare (Part A and Part B). To enroll in any Medicare Advantage plan, you must first have both Medicare Part A and Medicare Part B. The Advantage plan then covers your Part A and Part B benefits (and usually more, like dental, vision, and hearing). If you want a Medicare Advantage plan, Part B is effectively mandatory for you, because without it you cannot join any MA plan.

Medicare Advantage Annual Enrollment Period (AEP) runs October 15 through December 7, 2026, with coverage starting January 1, 2027. The Medicare Advantage Open Enrollment Period (OEP) runs January 1 through March 31, 2026, and allows one plan switch. Both require active Part B enrollment as a prerequisite. Dual-eligible beneficiaries (those with both Medicare and Medicaid) often have access to Dual Eligible Special Needs Plans (D-SNPs) that coordinate both programs, and these also require active Part B enrollment.

What Part B Covers and Why Most Beneficiaries Need It

Medicare Part B covers two broad categories: medically necessary services (doctor visits, outpatient surgery, mental health services, ambulance services, durable medical equipment) and preventive services (annual wellness visits, cancer screenings, flu shots, cardiovascular screenings). The 2026 Part B deductible is $283. After meeting the deductible, Medicare Part B pays 80% of the Medicare-approved amount, and you pay the remaining 20% coinsurance with no cap unless you have Medigap or Medicaid.

The unlimited 20% coinsurance is the main financial risk of not having supplemental coverage alongside Part B. Medigap (Medicare Supplement Insurance) plans pick up the 20% coinsurance for most covered services. Without Part B altogether, you bear the full cost of outpatient care. For context: a single hospitalization-associated outpatient procedure can run $10,000 to $50,000 at billed charges, and 20% of even the Medicare-approved amount can be significant. Most people 65 and older who have no employer coverage find that Part B is economically essential even if not legally required.

How to Enroll in Medicare Part B in 2026

Medicare Part B enrollment in 2026 starts at medicare.gov or by calling Social Security at 1-800-772-1213. For those not automatically enrolled (not yet receiving Social Security), the SSA handles Part B enrollment directly. The enrollment form is CMS-40B (Application for Enrollment in Medicare Part B). You can apply online at ssa.gov, by phone, or in person at a Social Security office.

• Step 1: Confirm your eligibility window. Check whether you are in your IEP (7-month window around your 65th birthday) or whether you have an SEP active because you recently left employer coverage.
• Step 2: Gather documents. You will need your Medicare card (or Part A award letter), proof of prior employer coverage if claiming an SEP (CMS-L564 form completed by your employer), and your Social Security number.
• Step 3: Submit CMS-40B to Social Security. Online at ssa.gov, by calling 1-800-772-1213, or in person at your nearest SSA office. If claiming a SEP, submit CMS-L564 simultaneously to document employer coverage.
• Step 4: Confirm your effective date. Coverage starts the first of the month after SSA processes your enrollment. Check Medicare.gov to confirm your Part B effective date after applying.
• Step 5: Choose supplemental coverage. After Part B is active, evaluate Medigap plans to cover the 20% coinsurance, or Medicare Advantage plans that bundle Part A, Part B, and usually Part D (drug coverage) into one plan.

Is Medicare Part B mandatory when you turn 65?

No. Medicare Part B is legally voluntary at any age, including when you turn 65. However, if you skip it and do not have qualifying employer coverage, you will pay a permanent late enrollment penalty of 10% per full year delayed when you do eventually sign up. For most people without active employer coverage, enrolling during the 7-month Initial Enrollment Period around their 65th birthday is strongly advisable.

What is the Medicare Part B late enrollment penalty in 2026?

The 2026 Part B late enrollment penalty is 10% of the standard monthly premium ($202.90) for each full 12-month period you were eligible but not enrolled. If you delayed 3 full years, your premium is 30% higher than the standard rate, permanently. Partial years do not trigger an additional penalty tier. The dollar penalty adjusts each year as CMS changes the standard premium.

Can I delay Medicare Part B if I have employer insurance?

Yes, but only if you are actively working (not retired) and your employer group health plan is through a company with 20 or more employees. When your employment or coverage ends, you have an 8-month Special Enrollment Period to sign up for Part B without penalty. COBRA does not count as active employer coverage for this SEP, and neither do retiree plans or individual market plans.

What happens if I miss my Initial Enrollment Period for Part B?

If you miss your IEP and do not have a qualifying SEP, you must wait for the General Enrollment Period (January 1 through March 31 each year). Coverage starts on the first of the month after you enroll. You will also owe the late enrollment penalty equal to 10% per full year delayed, and that surcharge is permanent for the life of your Part B coverage.

Is Medicare Part B required to join Medicare Advantage?

Yes. To enroll in any Medicare Advantage (Part C) plan, you must already have both Medicare Part A and Medicare Part B. If you decline Part B, you are ineligible for Medicare Advantage. The 2026 Medicare Advantage Annual Enrollment Period runs October 15 through December 7, 2026 with coverage beginning January 1, 2027.

Does COBRA let me delay Medicare Part B without a penalty?

No. COBRA is continuation coverage after you leave a job, not active employer coverage. CMS rules are explicit: only a group health plan through current employment qualifies for the Part B delay exception. If you rely on COBRA instead of enrolling in Part B during your IEP, you will face the late enrollment penalty when you eventually sign up.

What does Medicare Part B actually cover in 2026?

Medicare Part B covers outpatient care including doctor visits, outpatient surgery, mental health services, lab tests, diagnostic imaging, ambulance services, durable medical equipment, and preventive services (flu shots, cancer screenings, annual wellness visits). The 2026 Part B deductible is $283. After the deductible, Part B pays 80% of the Medicare-approved amount; you pay the 20% coinsurance with no annual cap unless you add Medigap or have Medicaid.

How much does Medicare Part B cost per month in 2026?

The standard 2026 Medicare Part B premium is $202.90 per month. Higher-income beneficiaries pay more through the Income-Related Monthly Adjustment Amount (IRMAA); for example, individuals with 2024 income above $106,000 pay a higher tier. If you have a late enrollment penalty, add 10% per delayed year to $202.90. Most beneficiaries have the premium deducted directly from their Social Security check.