Still working at 65: can you delay Medicare Part B? Start with the size of your employer

Your birthday falls on a Wednesday, and you go to work

You turn 65 on a Wednesday. You drive in, park in the same spot, swipe the same badge. Your health card has not changed. Nothing feels different.

But a clock started months ago. Your seven-month Medicare window opened three months before this birthday, and it will close three months after, whether you use it or not.

So you ask the obvious question at lunch. A coworker says you don't need Part B while you work. Another says you do. Your brother-in-law says it depends. He is the closest to right, and the least helpful.

What nobody says out loud is this: most people at 65 have no idea how many people their company employs. Yet that one number decides most of the answer.

Why "you're covered at work, you're fine" is only half a rule

The usual advice is true for many people. It is not true for everyone. The gap is in two words: "employer size" and "current."

Here is the part nobody mentions. When you have Medicare and a job plan, one of them pays your bills first. That one is the primary payer. The other is the secondary payer. It pays only for costs the first one didn't cover, and it might not pay all of them.

Medicare's rule, from the 2027 handbook and the Who pays first page, sets the line at 20 employees:

• 20 or more employees: the job's plan pays first. Medicare pays second.
• Fewer than 20: Medicare pays first. The job's plan pays second.

There is a twist. A small employer that is part of a multi-employer plan with 20 or more workers in total is generally treated like a big one. And that kind of plan can ask CMS to exempt its small employers. Then Medicare pays first again. Ask the plan if it has done this.

At a small employer, the stakes are clear. Medicare says job coverage "might not pay for health services if you don't have both Part A and Part B." CMS adds that most small-employer plans "require people to sign up for Part A and Part B as soon as they're eligible."

The word "current" matters just as much. These do not count as coverage from current work: COBRA, retiree coverage, VA coverage, a plan you bought yourself, and coverage you get through severance or a layoff.

One letter from your benefits office changes the whole picture

Here is the idea we would hand you first. Before you read another rule, get the employer size in writing.

Ask your benefits office one question: "Does the company have 20 or more employees for Medicare purposes?" Then ask a second: "Does the plan expect me to have Part A and Part B at 65?" Ask them to write the answers down.

With those two answers, the rest of the rules sort themselves out.

If you put off Part B because of job coverage, you get a Special Enrollment Period. That is a sign-up window outside the usual dates. You can sign up any time while you are still covered. Or you can sign up in the 8 months that start the month after the job ends or the coverage ends, whichever comes first.

The book gives a plain case. Your last day at work is in June. The plan keeps you covered through July. The job ended first, in June, so your 8 months run from July through February.

Signing up in that window usually means no Part B late penalty. It doesn't apply if your Medicare is based on End-Stage Renal Disease, or while you are still inside your first seven-month window.

When you are ready, two forms come into it. CMS-40B asks for Part B. CMS-L564 has a section for you and a section for your employer. Part B then generally starts the first of the month after you sign up. You can ask to push that start back up to 3 months, to line it up with the date your job plan stops.

CMS's notes on Medicare enrollment for employers cover the same ground from the employer's side.

The clocks that keep running while you work

Three more things move while you are at your desk.

Your Medigap window waits. It does not start at 65 if you put off Part B. It starts in the first month you have Part B and are 65 or older.

Your drug coverage needs a letter. If your job's drug plan is "creditable," it may let you wait on Part D with no penalty. The plan must tell you whether it is. Keep that letter.

And the HSA. If you or your employer put money into a Health Savings Account, the 6-month reach-back of Part A can make some of it excess, which is taxed. We cover that on the HSA page.

Before your last day at work

When you know your last day, a few jobs are worth doing early. These come from the book's still-working chapter.

1. Write down two dates. Your last day at work and your last day of job coverage. The one that comes first starts your 8-month window the month after.
2. Ask for Section B of Form CMS-L564 early. Your employer or its plan fills it out. If they can't, Social Security accepts other proof, such as W-2s, pay stubs or a health card with a start date.
3. Pick your Part B start date. You can ask to delay it up to 3 months, to line up with the day the job plan stops.
4. Find your drug coverage letter. It shows whether your job's drug coverage was creditable.
5. Stop HSA deposits in time, if you or your employer put money into one.
6. Make two calls to 1-800-MEDICARE. If your group health plan coverage ends, call to update your record. If you are retiring, call to make sure your primary insurance information is right.

Keep proof of the date you apply for Part B, such as the online confirmation or the name of the person you spoke with.

Where the book picks up the still-working case

This is the problem The Year You Turn 65 was written for. Nancy Whitaker puts the whole case in one place and lets you fill it in.

Still Working at 65 has the who-pays-first table with the multi-employer row, the list of coverage that does not count, the 8-month window with its example, both forms and the 3-month start option. It ends with a fill-in page for your own dates.

Seven Months Before You Apply: The Money Account That Has to Stop does the HSA math, month by month, with the IRS limits for 2025 and 2026.

Your Spouse's Clock Runs Separately covers the case where the job plan belongs to your spouse. The 20-employee line then applies to your spouse's employer.

The book is not affiliated with Medicare or Social Security, and it does not tell you whether to delay. Your State Health Insurance Assistance Program (SHIP) offers free counseling, and Social Security can look at your own file and confirm your 8-month dates.