Do I Have to Sign Up for Medicare at 65 If I'm Still Working?

No, not necessarily. If you or your spouse are still working, you are covered by that employer’s group health plan, and the employer has 20 or more employees, you can delay Medicare Part B for as long as the job lasts and sign up later with no late enrollment penalty (Medicare.gov).

That single sentence carries three conditions, and every expensive mistake people make at 65 comes from missing one of them. The coverage has to be based on current employment, so COBRA and retiree plans do not count. The employer has to be large enough that its plan pays before Medicare, and 20 employees is the line. And “delay” is a decision about Part B and Part D specifically; Part A usually still makes sense at 65, unless you are funding a Health Savings Account.

Nearly one in five Americans 65 and older is still in the labor force, and Florida is no exception: the Bureau of Labor Statistics counts about 919,000 working Floridians aged 65 and over in 2024. So this is not an edge case. It is the question a large share of people turning 65 in Tampa Bay actually have, and the answer is worth getting exactly right, because a wrong turn here is a penalty that lasts as long as you have Medicare.

The 20-employee rule decides who pays first

Medicare and an employer plan do not split the bill; one of them is the primary payer and the other fills in behind it. Which one goes first depends on the size of the employer, and that in turn decides whether delaying Part B is safe.

Source: Medicare.gov, who pays first; Medicare.gov, working past 65.

The first row is the one most people are picturing when they ask the question, and for them the answer is genuinely relaxed. The group plan is primary, Medicare would only pick up scraps behind it, and paying $202.90 a month in 2026 for Part B on top of your payroll deduction buys very little. Medicare.gov’s own wording is that you “can wait until you (or your spouse) stop working (or lose your health insurance, if that happens first) to sign up for Part B” and “won’t pay a late enrollment penalty.”

The second row is where the trap is. A small employer’s plan is secondary to Medicare once you turn 65, whether or not you have enrolled. If you never signed up, there is nothing in front of it, and the plan can process claims as if Medicare had paid its share. You are then responsible for the part Medicare would have covered. That is why the official guidance for employers under 20 is to ask the benefits administrator whether you need Part A and Part B at 65; in practice the answer is almost always yes.

What “still working” has to mean

The protection comes from coverage that is based on current employment, yours or your spouse’s. Three arrangements look like employer coverage and are not:

COBRA. When you leave a job you may be offered continuation coverage. It feels like the same insurance, and often it is the same card. But CMS is explicit that “COBRA coverage isn’t considered coverage based on current employment,” so it does not give you a Special Enrollment Period, and Medicare.gov adds that choosing COBRA does not extend the 8 months you have after the job ends. Worse, if you are Medicare-eligible and not enrolled, COBRA “may only pay for a small portion of the health care services you get, and you may have to pay most of the costs yourself” (Medicare.gov).

Retiree coverage. Same logic. Medicare pays first, the retiree plan pays second, and the plan “might not pay your medical costs during any period when you were eligible for Medicare but didn’t sign up for it” (Medicare.gov). Many retiree plans also require you to hold Part A and Part B to keep the retiree benefit at all.

A plan you bought yourself. If you are self-employed and cover yourself through the marketplace or an individual policy, that is not a group health plan and there is no Special Enrollment Period at the end of it. Medicare.gov’s instruction for this group is to sign up at 65.

Coverage through a spouse’s current job does count, and it counts regardless of which of you is 65. A 66-year-old on a 58-year-old spouse’s plan at a large employer can delay Part B just as safely as if the job were their own.

Should you take Part A at 65 anyway?

Usually yes. Part A, the hospital side, is premium-free for anyone who has paid Medicare payroll taxes for 40 quarters, or whose spouse has, and holding it alongside an employer plan costs nothing. If you are already collecting Social Security when you turn 65, CMS enrolls you in Part A and Part B automatically, and you then decide whether to keep Part B. If you are not collecting benefits yet, nothing happens until you apply. Not sure whether you qualify for premium-free Part A? The Part A premium checker walks through the quarters rule.

There is one group that should not take Part A at 65, and it is a big one among people still working.

The HSA rule that catches people

If you contribute to a Health Savings Account through a high-deductible health plan, enrolling in any part of Medicare ends your eligibility to contribute. The IRS puts it plainly in Publication 969: “Beginning with the first month you are enrolled in Medicare, your contribution limit is zero.” Part A alone triggers it.

The part people miss is the backdating. When you apply for Medicare or Social Security after 65, Part A is made retroactive, up to six months back, and Publication 969 says the zero-limit rule “applies to periods of retroactive Medicare coverage.” Contributions you made in those months become excess contributions with a tax penalty attached. That is why Medicare.gov’s instruction is that “you and your employer should stop contributing to your HSA 6 months before you retire or apply for benefits from Social Security.”

For 2026 the amounts at stake are real: the HSA limit is $4,400 for self-only coverage and $8,750 for family coverage, plus a $1,000 catch-up for anyone 55 or older (IRS Publication 969). Someone planning to retire in June who keeps contributing until May has six months of excess contributions to unwind.

The clean sequence for an HSA contributor working past 65 at a large employer is: decline both Part A and Part B at 65, keep contributing, stop contributions six months before the retirement date, then enroll in A and B through the Special Enrollment Period. The money already in the account is unaffected. You can keep it, invest it, and spend it tax-free on qualified medical expenses, including Medicare premiums, for the rest of your life.

What delaying Part B costs if you get it wrong

The Part B late enrollment penalty is “an extra 10% for each year you could have signed up for Part B, but didn’t,” measured in full 12-month periods, and you pay it for as long as you have Part B (Medicare.gov). It is calculated on the standard premium, so it grows every year the premium does.

Based on the 2026 standard Part B premium of $202.90 (CMS). Medicare.gov’s own example is the two-year row: a 20% penalty adds $40.58 a month for a total of $243.50. The 20-year column holds the 2026 premium flat, which understates the real cost, because the penalty is a percentage of whatever the premium is in each future year.

The important thing about this table is who it applies to. A person on a large employer’s group plan who delays Part B for three years is not in the 30% row; they are in the 0% row, because the Special Enrollment Period wipes out the penalty. The 30% row belongs to the person who assumed COBRA or a retiree plan was protecting them. You can run your own months against the rule with the Part B penalty calculator.

The General Enrollment Period is the backstop for anyone who misses their window: January 1 to March 31 each year, with coverage starting the month after you sign up. It does not remove the penalty.

Don’t forget Part D and the 63-day clock

Part B gets the attention, but the drug-coverage rule runs on a different, shorter clock and it is the one people more often trip over.

You can delay Medicare drug coverage without penalty only if the employer plan’s drug coverage is creditable, meaning it is “expected to pay, on average, at least as much as Medicare drug coverage” (Medicare.gov). Your employer must tell you each year whether the plan is creditable, in a Notice of Creditable Coverage it sends each year. Keep it. A Part D plan can ask you to prove creditable coverage later, and if you cannot, it charges the penalty.

Once you are eligible for Medicare, any stretch of 63 or more consecutive days without creditable coverage or a Medicare drug plan starts the penalty. It is 1% of the national base beneficiary premium, $38.99 in 2026, for every uncovered month, added to your Part D premium for as long as you have drug coverage. Medicare.gov’s example is 14 uncovered months producing a 14% penalty, about $5.50 a month at the 2026 base (Medicare.gov). Smaller than the Part B penalty, but permanent, and easy to avoid.

The practical consequence is that when your employer coverage ends, the Part D decision cannot wait the full eight months. Losing creditable coverage opens a Special Enrollment Period to join a drug plan, and the 63-day count starts at the same time. Line the drug plan up so it begins the month the employer coverage stops. The Part D penalty calculator shows what a gap would cost.

The 8-month Special Enrollment Period, step by step

When the job ends, or the group coverage ends, whichever happens first, the clock starts. You have eight months to sign up for Part B, or for Part A and Part B together, without penalty. You can also sign up at any point while still covered, which is what most people do a month or two before a planned retirement date so that Medicare starts the day the employer plan stops.

1. Fill out form CMS-40B, the Application for Enrollment in Medicare Part B. If you never took Part A either, you apply for both through Social Security instead.
2. Give form CMS-L564, Request for Employment Information, to your employer. You complete Section A; “the employer completes all of Section B,” confirming the dates you were covered under the group plan and the dates of employment (CMS). If you were covered through a spouse, their employer fills it in.
3. Send both forms to your local Social Security office, by mail, fax, or through Social Security’s online Part B enrollment. The forms go to the field office that serves your address.
4. Coverage begins the first of the month after Social Security receives your completed forms (Medicare.gov). Submit in the month before you want it to start, not the month of.

Two things do not restart or extend the clock. COBRA does not, as covered above. And a gap of more than eight months between group coverages is not bridged: the L564 form specifically asks Social Security to confirm continuous group coverage with no break longer than eight months. If you left one employer, took a year off, and joined another, the year off was unprotected.

Your Medicare Initial Enrollment Period, by contrast, is the seven months around your 65th birthday, three before and three after, and it runs whether or not you use it. The enrollment window checker will lay out both windows against your actual dates, and the Medicare enrollment periods guide covers each one in depth.

Working past 65 in Florida: the Medigap window most people miss

Florida has a large working-past-65 population. In 2024, 18.6% of Floridians aged 65 and over were in the labor force, about 942,000 people, of whom about 919,000 were employed, out of a 65-plus population of roughly 5.05 million (BLS, 2024 state tables). Nationally the 2025 rate was 19.1% (BLS, May 2026).

For that group, the retirement date matters for a second reason that has nothing to do with penalties: it is when the Medicare Supplement window opens.

Your six-month Medigap Open Enrollment Period, when a carrier must sell you any plan it offers without health questions, begins the first month you are 65 or older and enrolled in Part B. If you delay Part B until 68 because of employer coverage, your Medigap window opens at 68, not 65. Florida’s Department of Financial Services states it as “6 months from the Medicare Part B effective date in which to obtain a guaranteed issue Medicare Supplement policy” (Florida DFS).

Florida then adds a protection of its own. Section 627.6741 of the Florida Statutes requires insurers to issue a Medicare supplement policy, without conditioning it on health status, to a Florida resident 65 or older with Part B who applies “during the 2-month period following termination of coverage under a group health insurance policy” (Florida Statutes 627.6741). That covers the common Florida case where someone took Part B at 65 for a small-employer plan, kept working for years on the group plan, and only now wants a Medigap policy: the six-month window from the Part B effective date is long gone, but the two-month window after the group coverage ends is still there.

Two details worth knowing. Florida requires Medigap policies to be priced on an issue-age basis, so a policy bought at 68 is priced at 68 for good; a later change of carrier is rated at the age you apply. And the two-month window is short. Someone who spends the first eight weeks of retirement sorting out Part B and only then thinks about a supplement can miss it, and would then face medical underwriting. The order that works is: Part B effective the month the group plan ends, Medigap application submitted in the same month, Part D plan starting the same day. We covered what happens after the window closes in what happens if you miss your Medigap window.

IRMAA: your last working year follows you into retirement

One more consequence of working past 65 arrives about a year after you stop. Part B and Part D premiums are income-adjusted, and Social Security uses your tax return from two years earlier to set them. For 2026 the surcharge starts above $109,000 of modified adjusted gross income for a single filer, based on 2024 income (SSA).

So a person who retires in 2026 at a $140,000 salary will see their 2027 Part B premium set from 2025 income, and their 2028 premium from 2026, both years in which they were still earning. The income is gone, the surcharge is not.

The fix exists but is not automatic. Social Security recognises “work stoppage” and “work reduction” as life-changing events, and form SSA-44 lets you ask for the premium to be recalculated on a more recent year’s income. The IRMAA calculator shows which bracket a given income lands in, and the IRMAA guide walks through the lookback and the appeal.

A checklist for the year you turn 65 while working

None of this is complicated once it is laid out against your own dates, but the dates are the whole point. The same person can be perfectly safe delaying Part B and dangerously exposed on Part D, or safe on both and about to trigger an HSA penalty, and the only way to know is to walk through the list.

If you are working past 65 in Tampa Bay or anywhere in Florida and want a second set of eyes on the timing, schedule a conversation with Virginia. It is a planning session, not a sales call, and the most useful outcome is often a one-page calendar of what to file and when.