🕐 The Seven Months
First, what this page is. A plain explanation of the deadlines around turning sixty-five, what happens when they are missed, and which kinds of coverage do and do not protect you. It is not medical, legal, insurance or financial advice, it was not written by an attorney or an accredited Medicare adviser, and nothing here tells you what your own situation will do. Every dollar figure named is the published 2026 figure and these change every year. Confirm anything here with 1-800-MEDICARE, Medicare.gov, the Social Security Administration, or your State Health Insurance Assistance Program before acting on it. SHIP counseling is free.
A man turns sixty-five in June. He is healthy, he still works, he has never had a claim worth mentioning, and the health plan he has had for nineteen years is perfectly good. So he does nothing, which is what a sensible person does about a thing that is working.
Nothing happens. Nothing happens the next month either. Nothing keeps on happening for about three years, and then he retires, and he signs up for Medicare, and a clerk somewhere runs a calculation, and from that day forward his premium is thirty per cent higher than his neighbor’s. Same coverage. Same doctors. Same everything. Thirty per cent, every month, until he dies.
He did not do anything foolish. He did not gamble. He simply did not know there was a clock, because nothing in his life had ever behaved like one.
The clock is called the Initial Enrollment Period, and it runs seven months. It opens three months before the month you turn sixty-five, it takes in your birthday month, and it closes three months after. That is the whole of it. Seven months, once, and it does not come around again.
Some people never have to think about this at all, and it is worth knowing which people. If you are already drawing Social Security when you turn sixty-five, you are enrolled in Parts A and B automatically. The card arrives without your doing anything. Everybody else has to sign up on purpose — and “everybody else” now includes a great many people, because a lot of us are working past sixty-five and claiming Social Security later than our parents did. The rule that protected our fathers by accident does not protect us.
One small oddity worth checking rather than assuming: if your birthday falls on the first day of a month, your Medicare dates can sit a month earlier than you would expect. Ask the Social Security Administration what your own dates are rather than counting on a calendar. It costs one phone call and it is the sort of thing that is very cheap to get right and very expensive to get wrong.
💸 What Late Costs, and How Long For
There are two separate penalties, they work differently, and most people have only ever heard of one of them.
Part B — the doctor-and-outpatient half — adds ten per cent of the standard premium for each full twelve-month period you could have had Part B and did not. Two years late is twenty per cent. Seven years late is seventy. And it stays on your premium for as long as you have Part B, which is to say for the rest of your life.
Now here is the part that turns a nuisance into a real bill, and it is the part nobody mentions. The penalty is not a fixed number of dollars. It is a percentage of a moving one. Every January, Medicare recalculates it against whatever the standard premium is that year. The standard Part B premium is $202.90 a month in 2026, up from $185.00 in 2025. So a penalty set in 2020 is bigger this year than it was last year, and it will be bigger again next year, and it will go on quietly growing for thirty years without anybody sending you a notice about it.
There is one mercy in the Part B rule and it is worth knowing: it counts only full twelve-month blocks. An eleven-month gap costs nothing at all.
Part D is the other one, and it counts differently. The prescription drug penalty is one per cent of the national base beneficiary premium — $38.99 in 2026 — for every full month you went without creditable drug coverage, rounded to the nearest ten cents and added to your monthly premium for as long as you have drug coverage at all. Not every year. Every month. A three-month gap costs something. A thirty-month gap costs ten times as much. The clock starts once you go sixty-three days or more in a row without creditable coverage after you were first eligible.
People hear “one per cent” and stop worrying, which is exactly the wrong reaction to a number that gets multiplied by however many months you were not paying attention. And it catches a particular sort of person hardest: the one who takes no medication at all, sees no reason to buy a drug plan, and is perfectly right about that for eight years, and then needs something.
If you qualify for the federal Extra Help program, you do not pay the Part D late penalty. That is worth checking before you assume anything, and SHIP will check it with you for nothing.
📋 The 2026 Numbers, Told Flat
I am going to be dull for a moment, and I would take it kindly if you let me. These are figures rather than arguments, they were published by the Centers for Medicare & Medicaid Services in November, and they change every single year. There is no way to make them charming that would not also make them less useful. Read them once, note which ones apply to you, and we will go back to talking like people.
Two things that are not obvious from that list. About ninety-nine per cent of people pay no premium at all for Part A, because they have forty quarters of Medicare-covered employment behind them — so when this page talks about a premium and a penalty, it is almost always talking about Part B. And the Part B figure above is the standard premium; people over certain income thresholds pay more under a separate surcharge, which stacks on top of any late penalty rather than replacing it. The two are independent, and a man can be carrying both.
That is the dull part done.
🧰 If You Are Still Working, There Is an Exception
There is a genuine exception, it protects a great many people, and it is narrower than almost anybody believes.
If you are covered by a group health plan based on current, active employment — your own or your spouse’s — at an employer that has twenty or more employees, you can delay Part B past sixty-five without any penalty at all. That is the exception. That is the whole exception.
When that employment ends, or when the group coverage ends, a Special Enrollment Period opens and gives you eight months to sign up for Part B without penalty. For drug coverage the window is much shorter: sixty-three days.
The clock starts earlier than people expect, and this is where good, careful people get hurt. The eight months begin when employment ends or when the employer group coverage ends — whichever comes first. Not when you feel retired. Not when the last plan you were on runs out. Whichever comes first.
Two words in that rule do all the work, and they are current and active. Somebody has to actually be going to work. The moment nobody is going to work, the coverage stops being the kind that protects you, no matter what it looks like on the insurance card, no matter that the deductible is the same and the network is the same and the card in your wallet has not changed.
⚠️ The Trap With a Kind Face
Here is the list of things that feel exactly like employer coverage and do not count:
- COBRA. It is continuation of coverage from a job you no longer hold. Electing it does not pause the eight-month clock — the clock started when the job ended.
- Retiree health coverage, even from a large former employer, even if it is excellent, even if you paid into it for thirty years.
- Health benefits attached to a severance package.
- A Marketplace plan.
- VA health care, for Part B purposes. VA drug coverage does count as creditable for Part D — but that is the drug half only, and the Part B clock keeps running.
The cruelest version of this is dressed up as a kindness, and it is common enough that agents see it every year. An employer offers a retirement incentive: take the package, and we will pay your COBRA for eighteen months. To a man of sixty-six that reads as a year and a half of free insurance and a generous send-off. What it actually is, if he takes it and stops there, is eighteen months of an eight-month clock running out behind his back. He has been handed the thing that looks most like protection and is not protection, and he has been handed it by people who meant well and did not know either.
I want to be plain about why this is worth an entire section. It is not that the rule is complicated. The rule is simple. It is that the rule is counterintuitive in exactly the direction a reasonable person is most likely to guess wrong. Everything about COBRA is designed to feel continuous. That is its whole purpose and its whole appeal. And the one thing Medicare cares about is the one thing COBRA cannot supply, which is somebody actually at work.
One practical thing, and it costs nothing. Employers and unions send out an annual notice telling you whether your drug coverage is creditable. Most people throw it away. It is the proof, and the person who has kept those notices in a folder has a much easier conversation later than the person who has to go and ask a company he left in 2019 to look up his file.
🏢 Fewer Than Twenty
There is a second version of this that hurts differently, and it is worse in one respect, because instead of costing you money later it can leave you uncovered right now without your knowing.
If the employer generally has fewer than twenty employees, Medicare usually pays first once you turn sixty-five, and the group plan pays second. That is the ordering. It does not matter what you assumed, and it does not matter that you have been paying premiums into the group plan the whole time.
So a man at a small firm who skips Part B because he has “coverage at work” is not only running up a penalty. He is walking around with a plan that is designed to be the second payer with no first payer behind it. The bills come in, and the plan pays its share, and the rest of it is his.
The question to put to your employer, and put it in writing so there is a record of the answer. How many employees does the company have for Medicare purposes, and does the group plan pay primary or secondary once I turn sixty-five? Two sentences. Ask by email so the answer arrives by email. A benefits administrator who has to write it down is a benefits administrator who goes and checks.
📅 If You Already Missed It
Then read this part and do not spend the afternoon on regret, because there is a thing to do and there is a season in which to do it.
If you are inside the eight-month Special Enrollment Period — that is, active employment or employer group coverage ended less than eight months ago — you are not late at all. The two forms are CMS-40B (your application for Part B) and CMS-L564, which is the one your employer signs to confirm you had group coverage based on active employment. File them with Social Security.
If that window is gone, the General Enrollment Period runs January 1 through March 31 every year. Coverage now begins the month after you sign up, which is a good deal better than it used to be. Expect the late penalty to apply.
If you were told something wrong by Social Security or Medicare and that is why you missed the window, there is a process called equitable relief. It exists, it works, and it is worth pursuing. Be told honestly: the burden of proof sits on you, and approvals are not common. It is a good reason to keep a note of who you spoke to and when.
One piece of advice that is worth more than it looks. If you are retiring and you will need that L564 signed, get it signed while you still work there. While there is a human being in the personnel office who knows your name, who can find your file in a minute, and who will do it as a favor rather than as a request from a stranger. Six months after you clear out your desk it is a different errand entirely, and sometimes the company has been sold.
🚪 The Six-Month Door
Now the door that most people never even hear about until it has already shut, which is the whole reason it belongs on this website.
A Medigap policy — a Medicare Supplement — is the private plan that covers the parts Original Medicare leaves to you. Federal law gives you one six-month open enrollment period for it, and it begins the first month you are both sixty-five or older and enrolled in Part B.
Inside those six months you have what is called a guaranteed issue right. The insurer cannot refuse you. It cannot charge you more because of your health. It cannot ask about the diabetes or the heart business or the operation you had in 2019, and it cannot make you sit out a waiting period for them.
Outside those six months, in most states, it can do all four.
It is one time only, and there is no annual version of it. Federal law provides no yearly Medigap open enrollment the way it does for drug plans. Once the six months have run, an insurer in most states may ask health questions, may price you accordingly, and may decline you outright. A few states go further than the federal floor — some require insurers to sell at any time, and some have a birthday rule that lets you switch once a year — so it is worth asking your own state insurance department what you have. But do not plan around a protection you have not confirmed you have.
There is a piece of good news buried in the timing, and it belongs to the people this page is hardest on. If you legitimately delayed Part B because you were working, your Medigap window starts when your Part B starts, not when you turned sixty-five. It waits for you. A man retiring at seventy with proper employer coverage behind him walks into his six months on the day his Part B begins, in good health, with the whole market obliged to sell to him.
That is the argument of this website in a single sentence, and it is not even about buying anything. Two men, same age, same health. One of them knew what month he was standing in.
🏦 The Six-Month Look-Back
The last one is not a penalty and it is not a window. It is a piece of arithmetic that reaches backwards, and it catches the most careful people on this page — the ones who kept working, kept saving, and did everything else right.
When you sign up for Medicare after sixty-five, premium-free Part A is made effective retroactively, up to six months back — though never earlier than the month you turned sixty-five. You do not choose this. You cannot decline it.
And once any part of Medicare is in effect, you are not allowed to contribute to a Health Savings Account. Not reduced. Not prorated for the month. Zero.
Put those two rules side by side and the trap is fully built. Medicare decides, after the fact, that you were covered from six months ago. The tax code decides, after the fact, that everything you and your employer put into the HSA during those months was an excess contribution. You did nothing wrong on any of the days it happened.
What to do about it is simple, which is the good news. Stop HSA contributions — yours and your employer’s — at least six months before you apply for Medicare or claim Social Security. And note that second one carefully: claiming Social Security enrolls you in Part A whether you were thinking about Medicare or not. For 2026 the HSA limits are $4,400 for self-only coverage and $8,750 for family, with a further $1,000 catch-up once you are fifty-five, and in the year you go onto Medicare your limit is prorated for the months you were still eligible. If you think you may already have overcontributed, that is a conversation for a tax preparer, and it is a much cheaper conversation than the alternative.
⚡ Why This One Is on the Fifty List
Most of what is on this website is a thing you buy — a bar, a lamp, a wrench, a jack. This one is not. There is nothing to buy at all. There is only a date, and the knowledge of what the date is for.
And that makes it the purest example of the argument, because the cost of learning it is zero and the cost of not learning it is charged to you monthly, forever, on a number that goes up every January while you are not looking.
The reason to read this at fifty-five rather than at sixty-five is not that you will remember every figure. You will not, and you do not need to. It is that at fifty-five you will read it calmly, decide that there is a clock, and put a note in whatever you keep notes in for the year you turn sixty-four. That is the entire task. One note, ten years early, written on an afternoon when nothing at all was happening.
The man in the first paragraph of this page was not careless. He was busy, and healthy, and had a plan that worked, and no one ever told him. That is the only thing this website has ever really been about.