Missed your Medicare Part B sign-up? How the late penalty works and what to do now

Three things to do this week

Breathe first. The penalty is real, but it is a known number, and you can work it out on paper.

1. Find out if you had job coverage from current work. If you or your spouse were still working, with a plan from that job, you may have an 8-month Special Enrollment Period. It starts the month after the job ends or the coverage ends, whichever comes first. Signing up inside it usually means no penalty.
2. If not, mark January 1 to March 31. That is the General Enrollment Period. It runs every year. Since 2023, coverage starts the month after you sign up.
3. Call Social Security and ask one question. "Is any sign-up window open for me, and on what dates?" Ask for the answer in writing. Write down the name of the person you speak with.

That is it for this week. The rest is math.

How the 10% penalty is counted

Your monthly Part B premium goes up 10% for each full 12-month period you could have had Part B and did not. You pay it for as long as you have Part B.

The word that matters is "full." The rule counts whole 12-month periods only.

A delay of 11 months adds nothing. A delay of 23 months counts as one period, so 10%. A delay of 24 months is two periods, so 20%.

In 2026, the standard Part B premium is $202.90 a month. Medicare's example adds the penalty to that standard amount. So a 20% penalty adds $40.58 a month. The CMS page on Part A and B sets out the same rule, and Medicare's page on avoiding penalties has the official wording.

The premium changes each year, so the dollar amount of the penalty changes with it.

The COBRA letter that started this

Maybe it went like this. You left your job at 64 and kept the old plan through COBRA. Same card. Same doctors. Your 65th birthday came and went, and nobody brought up Part B.

Then a letter says COBRA ends this month. You call Social Security, and you learn that no window opened when COBRA ended. To Medicare, COBRA is not coverage from current work. The 8-month clock started when the job ended, not when COBRA did.

CMS warns that a person on COBRA who doesn't sign up when first eligible "may have to pay a life-long late enrollment penalty." The usual advice never mentions this case, which is why we put it here.

It is not your fault that the card looked the same. It is a rule most people only meet once.

When the penalty may not apply

The penalty is not automatic in every case. These are the cases the book and Medicare name.

• Job coverage from current work. Sign up inside the 8-month window after the job or the coverage ends, and there is usually no penalty.
• A Medicare Savings Program. These state programs help pay Medicare costs for people with limited income and savings. Medicare says you generally won't pay the Part B penalty if you enroll in one. You apply through your state's Medicaid office. Medicare says to apply even if you don't think you qualify.
• Something outside your control. Since January 1, 2023, CMS lists special sign-up windows for exceptional conditions, with no Part B late penalty. They are shown below.
• Disability Medicare before 65. If you paid a Part B penalty on disability Medicare, it stops in the month you turn 65. Ask Social Security to confirm that in writing.

If one of these fits you, say so when you call Social Security.

One more penalty that runs on its own

Part D, the drug coverage, has a separate penalty. It starts building if you go 63 days or more in a row without Medicare drug coverage or other coverage Medicare counts as "creditable." In 2026 it is figured from a national base of $38.99. Twenty uncovered months would add $7.80 a month.

So when you fix Part B, look at drug coverage in the same call.

Where the book helps from here

This is the problem The Year You Turn 65 was written for. Nancy Whitaker's book lays out every Medicare clock with its own dates, so you can see which ones are still open.

Three Months Out: The Seven-Month Window Opens has the window, the General Enrollment Period, the full 12-month rule and the 2026 penalty box.

Still Working at 65 covers the 8-month window, what counts as current work, and the two forms Social Security uses.

Leaving COBRA, Retiree Coverage, or the Marketplace walks the COBRA case month by month, including the 2-month window for drug and Advantage plans after old coverage ends.

The book is not affiliated with Medicare or Social Security. Your State Health Insurance Assistance Program (SHIP) gives free counseling if you think you missed a window, and Social Security can look at your own file and tell you which window, if any, is open.