Most people turning 65 know they should sign up for Medicare. Fewer realize that skipping Part B, even for good reasons, can quietly add a surcharge to your premium that never goes away. The rule is simple, but the exceptions are where people get caught.

What the Part B Late Enrollment Penalty Is

If you don’t sign up for Part B when you first become eligible and you don’t have qualifying coverage, Medicare adds 10% to your monthly premium for each full 12-month period you could have enrolled but didn’t. For most people, that is a lifetime penalty. It is calculated on the standard premium, which is $202.90 a month in 2026, so it grows whenever the standard premium rises.

Your Initial Enrollment Period lasts seven months: three months before the month you turn 65, your birthday month, and three months after. Miss it without coverage that qualifies you for a Special Enrollment Period, and the clock starts running.

What the Penalty Costs in 2026 (Worked Examples)

Here is the math using the 2026 standard premium of $202.90. Only full 12-month periods count, so waiting 23 months costs the same as waiting 12.

Months you waited	Penalty	Added each month	Total Part B premium	Extra per year
12 to 23	10%	$20.29	$223.19	$243.48
24 to 35	20%	$40.58	$243.48	$486.96
36 to 47	30%	$60.87	$263.77	$730.44
60 to 71	50%	$101.45	$304.35	$1,217.40

The 24-month row matches Medicare’s own example: 20% of $202.90 is $40.58, for a total of about $243.50. Someone who waits five years, enrolls at 70 and lives to 90 would pay that extra $1,217 a year for about 20 years, roughly $24,000 at today’s premium and more if the standard premium rises.

Who Can Delay Part B Without a Penalty

You can generally wait if you or your spouse are still actively working and covered by a group health plan through that job. Once the job or the coverage ends, you get a Special Enrollment Period:

• It starts the first month after your Initial Enrollment Period ends.
• It ends 8 months after the group health coverage or the employment ends, whichever happens first.
• Coverage generally starts the month after you sign up. If you enroll while still working or in the first full month after coverage ends, you can ask to delay the start by up to 3 months.

Medicare notes that COBRA does not count as group health plan coverage here, and getting COBRA does not extend your 8 months.

Who Usually Can’t Delay

Coverage that does not protect you from the penalty includes:

• Retiree coverage from a former employer.
• COBRA, even if it feels like active coverage.
• A job with fewer than 20 employees. In that case Medicare typically pays first, so skipping Part B can leave you with big gaps. Ask the employer to confirm in writing.
• Marketplace plans bought on your own, which do not give you a Special Enrollment Period for Part B.

The 20-employee rule is where most surprises happen, so confirm your employer’s size with the benefits office before you decide.

Quick Checklist: Should You Enroll in Part B Now?

1. Still working, employer has 20 or more employees, and you are on its plan? You can likely wait. Ask HR to confirm the plan counts as creditable group coverage.
2. Retired, on COBRA, or on retiree coverage? Enroll during your Initial Enrollment Period. Waiting risks the penalty.
3. Employer has fewer than 20 employees? Plan to enroll at 65, since Medicare usually pays first.
4. Your job or coverage ends soon? Mark the date 8 months out. That is your last penalty-free day.
5. Low income? A Medicare Savings Program can pay your Part B premium, and enrolling in one generally means no penalty.

How the Part A and Part D Penalties Compare

Part	Penalty	How long it lasts
Part A (only if you must buy it)	10% higher premium	Twice the number of years you waited
Part B	10% per full 12 months	As long as you have Part B
Part D	1% of the national base premium per month without creditable coverage	As long as you have drug coverage

Most people get Part A premium-free, so the Part A penalty rarely applies. The Part D penalty is based on a $38.99 national base premium in 2026. For example, a 14% penalty adds about $5.50 a month.

If You Already Missed Your Window

You can still sign up during the General Enrollment Period, January 1 to March 31 each year. Coverage starts the month after you sign up, and the penalty applies unless an exception covers you. If you qualify for a Medicare Savings Program, ask your state program about it, because that route can remove the penalty.

Frequently Asked Questions

Does the penalty ever go away?

For most people it does not. Medicare describes it as a lifetime penalty, and it is recalculated as the standard premium changes.

Is the penalty added to my income-related premium too?

The late enrollment penalty is a separate surcharge. Higher earners may also pay an income-related amount on top.

Where can I get help deciding?

Your state’s SHIP counselors give free, unbiased Medicare help, and Medicare.gov has the official rules. Check your own situation there before you delay.

The Rows the Table Skipped, and a Rounding Note

The table above leaves out the 48 to 59 month row. Using the same 2026 premium of $202.90, waiting that long means a 40% penalty: $81.16 added each month, a total Part B premium of about $284.06, and about $973.92 extra per year. Medicare.gov shows its own two-year example as $243.48 and then rounds the monthly premium to $243.50, so the amount on your Social Security statement may differ from these figures by a few cents.

Worked Example: Counting Your Own Months

Assume Marcus turned 65 in June 2024. His seven-month Initial Enrollment Period ran from March through September 2024. He retired in 2024, took COBRA instead of enrolling, and then decided to join Part B during the General Enrollment Period in March 2027. These are made-up dates to show the counting.

1. His Initial Enrollment Period ended in September 2024.
2. He had no qualifying coverage from October 2024 until he signed up in March 2027, about 29 months. COBRA does not count.
3. Only full 12-month periods count, so that is 2 full periods, or a 20% penalty.
4. On the 2026 premium of $202.90, the penalty is $40.58 a month, for a total of about $243.48 a month. Because the penalty is a percentage of the standard premium, it rises when the premium does.
5. Coverage would begin the month after he signs up, in April 2027.

Had Marcus been covered by an active employer plan and enrolled within 8 months of that job ending, with proof of coverage, he would have owed no penalty at all. And if he had waited fewer than 12 full months past his Initial Enrollment Period, no 10% charge would have started, because only full 12-month periods count.

Timeline If You Are Still Working at 65

When	What to do
3 months before your 65th birthday month	Initial Enrollment Period opens. Confirm with HR whether your employer plan is the kind that lets you delay Part B.
Birthday month and 3 months after	Initial Enrollment Period continues. If you are covered through an employer with 20 or more employees, you can generally keep working without Part B.
Last month of your job or employer coverage	Ask your employer to complete the Request for Employment Information (form CMS-L564) so you have proof of your coverage dates.
Within 8 months after the job or coverage ends	Apply for Part B with the Application for Enrollment (form CMS-40B) plus the employer form, or enroll through ssa.gov. This is your penalty-free window.
If you miss it	Wait for the General Enrollment Period, January 1 to March 31. Coverage starts the month after you sign up, and the penalty can apply.

If your former employer cannot complete the form, the Medicare Rights Center suggests contacting them for other options, and AARP lists substitutes such as pay stubs or W-2s that show health premiums were deducted. Ask the Social Security Administration (1-800-772-1213) which documents it accepts for your case.

Common Mistakes That Trigger the Penalty

• Counting COBRA or retiree coverage as if it were active-employee coverage.
• Assuming that a small employer’s plan lets you delay. With fewer than 20 employees, Medicare typically pays first.
• Waiting until the employer plan ends and then missing the 8-month window.
• Skipping the paperwork. Without proof of coverage dates, Social Security may charge a penalty you could have avoided.
• Assuming a Medicare Savings Program is automatic. You have to apply through your state, so ask your State Health Insurance Assistance Program counselor for free help.