Part B penalizes late sign-ups, and the extra cost does not go away. Here is how the penalty is figured, when waiting is allowed, and what a two-year delay adds to your monthly premium.

This guide is general information, not insurance, tax or legal advice. Rules, limits and deadlines change each year, so check HealthCare.gov, Medicare.gov or your insurer for your situation.

Medicare Part B pays for doctors’ services and outpatient care, and the timing of your sign-up has a price attached. Miss your window and a percentage penalty gets added to your monthly premium, in some cases permanently. The penalty is predictable, though, and it catches most often those who did not know they could have delayed for free.

What Part B Covers and Why Enrollment Timing Matters

Part B covers physicians’ services, outpatient hospital care, certain home health services and durable medical equipment, according to the Centers for Medicare & Medicaid Services (CMS), and you pay a monthly premium for it. The standard premium for 2026 is $202.90, one of the figures CMS announces each year. If words like premium and coinsurance feel fuzzy, our health insurance terms guide defines them.

Most people become eligible at 65. The Initial Enrollment Period lasts 7 months: it starts 3 months before the month you turn 65 and ends 3 months after that month. Coverage starts on the first of a month, with the exact date depending on which month of the window you chose. People who claim Social Security before 65 are enrolled in Parts A and B automatically, so the penalty question mainly affects everyone else. Our Medicare basics guide explains how Parts A, B, C and D fit together. Part A is separate for most people: roughly 99% of beneficiaries pay no premium for it because they or a spouse have at least 40 quarters of Medicare-covered employment.

How the Late-Enrollment Penalty Is Calculated

The Part B penalty equals 10% of the standard monthly premium for every complete 12-month stretch in which you were eligible for Part B but stayed unenrolled. Two details matter. First, only whole 12-month blocks count, so a 14-month delay means one period, not a penalty for every month you waited. Second, the extra amount generally remains on your premium for as long as you keep the coverage.

Against the 2026 standard premium of $202.90:

Months of delay	Full 12-month periods	Penalty added	Monthly total
14	1	$20.29 (10%)	$223.19
24	2	$40.58 (20%)	$243.48
25	2	$40.58 (20%)	$243.48

The last two rows match on purpose. Someone 25 months late pays the same penalty as someone 24 months late, because partial periods do not count.

When You Can Delay Without a Penalty

If either you or your spouse remains employed and health insurance comes from that job, you can generally put off enrolling in Part B without a penalty. You can hold off until you stop working or lose that coverage, whichever happens first, and an 8-month Special Enrollment Period follows. The clock starts when the employment or coverage ends, even if you pick COBRA or other non-Medicare coverage in the meantime. COBRA is a bridge after a job loss, but it does not give you the same delay rights; our article on COBRA versus the Marketplace explains how it works.

Two cases need extra caution. Retiree coverage from a previous job does not let you delay Part B penalty-free, and it may not pay for your services unless you have both Part A and Part B, so ask your benefits administrator how it coordinates with Medicare. If you are self-employed, or your plan is not offered to everyone at the company, ask whether the IRS would classify it as an employer group health plan. If not, sign up at 65.

Important: COBRA and retiree plans get different treatment from active employer group coverage. Relying on either one can leave you with a permanent penalty, so confirm your situation before your Initial Enrollment Period ends.

What Happens If You Miss Every Deadline

Miss the Initial Enrollment Period and any Special Enrollment Period, and your options narrow. You can sign up during the General Enrollment Period, which runs from January 1 to March 31 each year, with coverage starting the month after you sign up. The open enrollment period from October 15 to December 7 cannot be used to join Part B; it only lets people who already have Medicare change drug or Medicare Advantage coverage. The delay can also leave you without coverage for months, paying full price for doctor and outpatient care. If you want Medicare to start when your job-based insurance ends, apply for Part B in the month before the month you or your spouse intend to retire, and submit the extra form showing you had job-based coverage while working.

A Worked Example of What Delaying Costs Over Time

Take someone who turns 65 with no qualifying employer coverage and does nothing, then joins during the General Enrollment Period two years later. The delay is 24 months, so the penalty is 20%, or $40.58 added to the $202.90 standard premium: $243.48 per month in 2026 figures, paid for as long as they keep Part B.

That figure covers the penalty alone. The delay also meant two years with no Medicare help for doctor and outpatient bills. And because the penalty is a percentage of the standard premium, it grows in dollar terms as CMS raises premiums, even though the percentage never changes. At $40.58 per month, a penalty carried for ten years adds roughly $4,870 to what you pay.

IRMAA and Where to Confirm Your Numbers

The standard premium is not the whole story on cost. Under the Social Security Act, CMS sets Part B premiums, deductibles and coinsurance amounts each year, and it also publishes income-related monthly adjustment amounts, the extra sums higher-income beneficiaries owe. The late-enrollment penalty is figured as a percentage of the standard premium, so the penalty and any income-related amount are separate parts of your monthly bill. Check the current income-related tables on Medicare.gov rather than relying on numbers you heard elsewhere.

Medicare.gov lays out the enrollment periods, and you can call 1-800-MEDICARE (1-800-633-4227; TTY users can call 1-877-486-2048) with questions. Social Security handles Part B sign-ups, and SHIP counselors in your state can help you review your timing for free. If you are within 3 months of turning 65 and not covered by an employer plan through current work, contact Social Security now to get your Part B application started.

Frequently asked questions

How is the Medicare Part B late-enrollment penalty calculated?
It is 10% of the standard monthly Part B premium added for every complete 12-month stretch you went without enrolling when you were eligible. Only whole 12-month blocks count, so a 14-month delay means one period, and the extra amount stays on your premium while you keep Part B.

Can I delay Part B if I am still working at 65?
When you or a spouse remain on the job with group health coverage from that employer, delaying Part B generally carries no penalty. You then have 8 months after the employment or coverage ends to sign up during a Special Enrollment Period.

Does COBRA coverage protect me from the Part B penalty?
No. Medicare guidance treats COBRA and retiree coverage differently from active employer group coverage, and neither lets you delay Part B penalty-free. The 8-month Special Enrollment Period clock starts when employment or coverage ends, even if you choose COBRA in the meantime.

What happens if I miss both my Initial Enrollment Period and any Special Enrollment Period?
You can sign up during the General Enrollment Period, which runs from January 1 to March 31 each year, and coverage starts the month after you sign up. You may also owe the late-enrollment penalty while you keep the coverage.