Social Security gives you room to change your mind. Medicare does not.
Your enrollment window opens and closes around your 65th birthday, and if you miss it, you can pay more for coverage every month for the rest of your life. Claiming Social Security later does not move that window by a day.
The companion piece covers the claiming decision. This one is about the clock that does not move.
Here is what matters, in the order it matters.
Your Seven-Month Window
Your Initial Enrollment Period runs seven months, opening three months before your birthday month, covering that month, and closing three months after. This is when you sign up for Original Medicare, meaning Part A and Part B.
Sign up before your birthday month and coverage starts the month you turn 65. Sign up during that month or later and it starts the month after that, so the back half of the window is not as safe as the front half.
Delaying Social Security changes none of this, so if you plan to claim SS at 70 your Medicare deadline is still 65.
There is also a case where you do nothing at all. If you are already receiving Social Security at least four months before you turn 65, Medicare enrolls you in Part A and Part B automatically and mails your card. That cuts both ways: early claimers can relax, and anyone who did not want Part B yet has to actively turn it down.
Still Working at 65
There is one real exception, and it comes with a size limit most articles skip.
If you or your spouse are still working and covered by an employer group health plan, you can delay Part B. When you leave, a Special Enrollment Period gives you eight months, counted from the day you stop working or the day coverage ends, whichever comes first.
The size limit is this. If the employer has 20 or more employees, the group plan pays first and Medicare pays second, so waiting works. If it has fewer than 20, Medicare pays first and CMS tells those workers to enroll in Part A and Part B at 65. Ask your HR department one question: does this plan have 20 or more employees behind it?
COBRA continuation coverage and retiree coverage do not count. Medicare says so plainly: “COBRA coverage doesn’t extend your limited time to sign up for Medicare.” This is the most expensive mistake we see.
Now watch the second clock: the Part B window after employer coverage ends runs eight months, but the window to pick up drug coverage runs only two full months after the month that coverage ends. Use month seven for Part B and the drug deadline has already passed, which starts a penalty that never goes away.
One more note if you fund a health savings account. Enrolling in any part of Medicare ends your ability to contribute, and Part A can be backdated up to six months, though never before your first month of eligibility. So CMS says to stop contributing six months before you sign up or apply for Social Security.
What Missing the Window Costs
Three penalties, and no two of them work the same way.
- Part B. Your premium rises 10% for every full 12 months you could have enrolled and did not. The 10% is figured on that year’s standard premium, so the dollar amount climbs as premiums do. At the 2026 standard premium of $202.90 a month, two years late runs about $40.58 extra a month and five years late runs about $101.45, for as long as you have Part B.
- Part D, which is prescription drug coverage. The trigger is 63 days or more without Part D or other creditable coverage, and creditable means the plan you already have is at least as good as Medicare’s. Your plan has to tell you in writing each year whether it counts. The penalty is 1% of the national base beneficiary premium, $38.99 in 2026, for every full month you went without, and it lasts as long as you have drug coverage.
- Part A. Most people get Part A free because they paid Medicare taxes for at least 10 years. If you have to buy it and you sign up late, the penalty works differently: you pay it for twice the number of years you delayed, not for life.
Both lasting penalties have an escape hatch. A Medicare Savings Program can eliminate the Part B penalty, and Extra Help waives the Part D one. Ask about both by name.
The Surprise Bill Nobody Warns You About
Enrolling on time does not guarantee you the standard premium. Above certain income levels Medicare charges more for Part B and Part D, and that surcharge is called the Income-Related Monthly Adjustment Amount, or IRMAA.
Four things about it catch people out.
- It looks back two years. Your 2026 premium comes from your 2024 tax return. A big year in 2024 lands in your Medicare bill long after you stopped thinking about the deal that caused it.
- The income it counts is wider than you expect: your adjusted gross income plus tax-exempt interest. Municipal bond interest that keeps your tax bill down does not keep IRMAA down.
- It is a cliff. In 2026 the surcharge starts once that income passes $109,000 for a single filer or $218,000 for a married couple filing jointly, and one dollar over the line costs you the full tier for the whole year.
- It applies to each person. At the top tier that runs $487 a month each for Part B and up to $91 each for Part D, so a couple can pay about $1,156 a month on top of the standard premiums.
If your income really has changed, you can ask Social Security to use a newer year. Form SSA-44 covers eight events: marriage, divorce or annulment, death of a spouse, work stoppage, work reduction, loss of income-producing property, loss of pension income, and an employer settlement payment.
A one-time windfall is not on that list, so a Roth conversion will not win this appeal and neither will a home sale.
The real relief is automatic. IRMAA is redetermined every year, so once your income drops back the surcharge comes off on its own. If you do have a qualifying event, file in the year your income drops, because a new determination is generally effective January 1 of that year.
Medicare Is Not Only an Age-65 Event
One more group needs this article and almost nothing written about Medicare speaks to them.
A person who has received Social Security disability benefits for 24 months gets Medicare automatically, at any age. Part A and Part B both, with the card arriving three months before the 25th month. Two conditions come sooner: ALS, also called Lou Gehrig’s disease, and permanent kidney failure.
In the families we work with, that pathway often runs through a parent. An adult who became disabled before age 22 can draw a benefit on a parent’s Social Security record once that parent starts retirement, disability benefits, or dies. Your claiming decision can start your child’s 24-month Medicare clock.
So the two halves of this article can reach one family at two different times. The IRMAA half is a parent problem that shows up in your sixties, and the enrollment half may already be your adult child’s reality, decades earlier.
If that is your household, the sequence matters more than either decision on its own. We cover the claiming side in the companion piece.
Why This Belongs With Your Social Security Strategy
The accounts you draw from set your taxable income and your taxable income two years later sets your Medicare premium. So the timing of a Roth conversion or a large capital gain is a Medicare decision, not only a tax decision.
A plan that optimizes your claiming age and ignores IRMAA is solving half the problem.
Next Step
Your enrollment date is set the day you turn 65. The income that will set your premium is still yours to shape.
Two things you can do tonight: put your seven-month window on a calendar, then pull your 2024 return and compare the income line to $109,000 or $218,000, because that number is already set for 2026.
If you want your withdrawals, your conversions, and your Medicare timing working together instead of against each other, a Trailhead Meeting is where we start.
Figures current as of August 2026. Medicare premiums, penalties, and IRMAA thresholds change annually. The 2027 figures are announced in the fall.