Medicare enrollment is time-gated, and signing up late means a penalty on your premium for life, unless a Special Enrollment Period or a Medicare Savings Program covers you.Centers for Medicare & Medicaid Services. (n.d.). Avoid late enrollment penalties. medicare.gov. Retrieved Jul 15, 2026, from https://www.medicare.gov/basics/costs/medicare-costs/avoid-penalties Most people get one clean shot at it: a seven-month window around their 65th birthday. But the right window depends on your situation, and they don't all work the same way. This guide walks through each enrollment period, when your coverage actually starts, and exactly what a late penalty costs, so you can make the call with confidence.
When to sign up for Medicare: the windows at a glance
Medicare has one window for first-time sign-up at 65, a special path for people still working, a backup window for people who miss their first chance, and two windows that only let you change coverage you already have. Here's how they line up.Centers for Medicare & Medicaid Services. (n.d.). Open Enrollment. medicare.gov. Retrieved Sep 2, 2026, from https://www.medicare.gov/health-drug-plans/open-enrollment,Centers for Medicare & Medicaid Services. (n.d.). When does Medicare coverage start?. medicare.gov. Retrieved Aug 9, 2026, from https://www.medicare.gov/basics/get-started-with-medicare/sign-up/when-does-medicare-coverage-start
| Window | When | What it's for |
|---|---|---|
| Initial Enrollment Period (IEP) | 7 months around your 65th birthday | First-time sign-up for Parts A and B |
| Special Enrollment Period (SEP) | While you have current-employer coverage, plus 8 months after it ends | Signing up after 65 if you delayed because you were working |
| General Enrollment Period (GEP) | January 1 – March 31 | Backup if you missed your IEP and have no SEP |
| Fall Open Enrollment | October 15 – December 7 | Changing coverage you already have |
| Medicare Advantage Open Enrollment | January 1 – March 31 | One change for people already in a Medicare Advantage plan |
| Medigap Open Enrollment | 6 months, starting when you're 65+ and enrolled in Part B | A one-time window to buy any Medigap policy an insurer sells, with no medical underwriting |
The Medigap row is the one people miss. During that one-time six-month window an insurer must sell you any policy it offers, can't use medical underwriting, and can't charge you more because you have health problems. One limit still applies: unless you had at least six months of continuous prior creditable coverage, the insurer can refuse to cover your out-of-pocket costs for a pre-existing condition for up to six months.Centers for Medicare & Medicaid Services. (2025). Choosing a Medigap Policy: A Guide to Health Insurance for People with Medicare (CMS/NAIC, 2025) - Medicare.gov. medicare.gov. Retrieved Aug 22, 2026, from https://www.medicare.gov/publications/02110-choosing-a-medigap-policy.pdf Miss the window and you can be medically underwritten or turned down later.
Your Initial Enrollment Period: the 7-month window
Your first chance to sign up is your Initial Enrollment Period, and for most people it's the only window they'll ever need. It runs for seven months: the three months before the month you turn 65, the month you turn 65, and the three months after. So if your birthday is in June, your window opens March 1 and closes September 30.Centers for Medicare & Medicaid Services. (n.d.). Open Enrollment. medicare.gov. Retrieved Sep 2, 2026, from https://www.medicare.gov/health-drug-plans/open-enrollment
Whether you have to do anything depends on Social Security. If you started receiving Social Security or Railroad Retirement benefits at least four months before you turn 65, you're enrolled in Part A and Part B automatically, and your welcome package with the card arrives in the mail about three months before coverage starts. If you're not yet collecting those benefits, or you claimed them only a month or two before 65, no one enrolls you. You have to sign up yourself through the Social Security Administration, online or by phone, during your window.Centers for Medicare & Medicaid Services. (n.d.). Open Enrollment. medicare.gov. Retrieved Sep 2, 2026, from https://www.medicare.gov/health-drug-plans/open-enrollment
A bit of timing detail worth knowing, and it works differently for the two parts. Coverage always starts on the first of a month. If you qualify for premium-free Part A, your Part A starts the month you turn 65 no matter which of the seven months you sign up in (and if your birthday falls on the first of the month, it starts the month before). Part B, and Part A if you have to buy it, follows your sign-up date instead: sign up in the three months before your birthday month and coverage starts the first day of your birthday month; sign up during or after your birthday month and it starts the first of the month after you enroll. Signing up early is the way to have Part B ready the day you turn 65.Centers for Medicare & Medicaid Services. (n.d.). Open Enrollment. medicare.gov. Retrieved Sep 2, 2026, from https://www.medicare.gov/health-drug-plans/open-enrollment
Let this window close without other qualifying coverage and you're in late-penalty territory. The one situation you can safely skip it for is next.
Still working at 65? You may be able to wait
Plenty of people are still working at 65 and covered by a job's health plan, either their own or a spouse's. If that coverage comes from a current employer, you can usually delay Part B without any penalty and sign up later, through a Special Enrollment Period. Not every job-based plan counts: Medicare gives this guidance for group health insurance that is available to everyone at the company, and tells people who are self-employed, or whose plan is not available to everyone at the company, to ask their insurance provider whether it is employer group health plan coverage as the IRS defines it, and to sign up at 65 if it is not. Part D runs on a separate clock: its penalty is triggered by going 63 days or more without creditable drug coverage, so check whether your employer drug coverage is creditable rather than assuming the Part B window covers it. One group is carved out entirely: this Special Enrollment Period does not apply if you're eligible for Medicare based on End-Stage Renal Disease (ESRD).Centers for Medicare & Medicaid Services. (n.d.). When does Medicare coverage start?. medicare.gov. Retrieved Aug 9, 2026, from https://www.medicare.gov/basics/get-started-with-medicare/sign-up/when-does-medicare-coverage-start
If you are under 65 and on Medicare because of a disability, read that "you or your spouse" more broadly. CMS titles this the Special Enrollment Period for the Working Aged and Working Disabled, and for the disabled half, coverage based on a non-spouse family member's current employment also qualifies. One condition bounds that route: the family member's plan has to be a large group health plan, which Medicare defines as one covering an employer or employee organization with at least 100 employees. Social Security describes the same thing from its side, saying people on Social Security disability benefits covered by a group health plan through their own or a family member's current employment have a special enrollment period and premium rights similar to those for workers 65 and older.Centers for Medicare & Medicaid Services. (n.d.). When does Medicare coverage start?. medicare.gov. Retrieved Aug 9, 2026, from https://www.medicare.gov/basics/get-started-with-medicare/sign-up/when-does-medicare-coverage-start
Here's how the timing works, per Medicare's working-past-65 rules. While you still have the current-employer coverage, you can enroll any time you like with no penalty. Once the job ends or that coverage ends, whichever comes first, you get an eight-month Special Enrollment Period to sign up for Part B. Medicare's own agencies state its start a month apart: CMS counts the eight months from the month the employment or the coverage ends, and Social Security counts from the month after. Count from the earlier one, so treat your window as closing eight months after the job or the coverage ends. Coverage under this Special Enrollment Period generally starts the first month after you sign up. If you sign up for Part B while you're still working, or within the first full month after the employer coverage ends, you can ask to delay your Part B start date up to 3 months. Many people still take premium-free Part A at 65 even while working, since it usually costs nothing.Centers for Medicare & Medicaid Services. (n.d.). When does Medicare coverage start?. medicare.gov. Retrieved Aug 9, 2026, from https://www.medicare.gov/basics/get-started-with-medicare/sign-up/when-does-medicare-coverage-start,Office of the Law Revision Counsel, U.S. House of Representatives. (n.d.). 42 U.S.C. 426 - Entitlement to hospital insurance benefits (OLRC prelim, rolling). uscode.house.gov. Retrieved Sep 2, 2026, from https://uscode.house.gov/view.xhtml?req=granuleid:USC-prelim-title42-section426&num=0&edition=prelim
One detail trips people up more than any other, so be clear on it: COBRA and retiree coverage do not count as current-employer coverage for this purpose. They're real insurance, but Medicare doesn't treat them as the kind of active employment coverage that protects you. They do not extend your eight-month window. If you retire and go on COBRA, your eight months still start ticking from the month your employment ended, not from when COBRA runs out. People who wait for COBRA to expire before enrolling routinely blow past the SEP and land a lifelong Part B penalty. When your job or job-based coverage ends, treat the eight-month clock as already running.Centers for Medicare & Medicaid Services. (n.d.). When does Medicare coverage start?. medicare.gov. Retrieved Aug 9, 2026, from https://www.medicare.gov/basics/get-started-with-medicare/sign-up/when-does-medicare-coverage-start
But don't read that as closing the door on severance. Social Security's own list of situations that may qualify you includes group health plan coverage based on severance or retirement pay, as long as the job that coverage is based on ended in the last eight months. So the question isn't whether severance money is paying the premium; it's whether the job ended inside that eight-month window. If it did, ask Social Security rather than assuming you're shut out.Centers for Medicare & Medicaid Services. (n.d.). When does Medicare coverage start?. medicare.gov. Retrieved Aug 9, 2026, from https://www.medicare.gov/basics/get-started-with-medicare/sign-up/when-does-medicare-coverage-start
Employer size matters too: it decides whether the employer plan or Medicare pays first, which changes whether delaying Part B is smart at all. Confirm yours before you wait.
The General Enrollment Period: your backup window
If you miss your Initial Enrollment Period and you don't qualify for a Special Enrollment Period, you're not locked out forever. There's a backup: the General Enrollment Period, which runs January 1 through March 31 every year. Anyone who needs Part A or Part B and missed their earlier windows can use it.Centers for Medicare & Medicaid Services. (n.d.). When does Medicare coverage start?. medicare.gov. Retrieved Aug 9, 2026, from https://www.medicare.gov/basics/get-started-with-medicare/sign-up/when-does-medicare-coverage-start
There's good news on timing here. Under section 120 of the Consolidated Appropriations Act, 2021, any GEP sign-up dated January 1, 2023 or later gets coverage starting the first day of the month after you enroll. That's a real improvement over the old rule, which left people waiting until July 1. The Social Security Administration confirms the change applies to all current GEP enrollments.Centers for Medicare & Medicaid Services. (n.d.). When does Medicare coverage start?. medicare.gov. Retrieved Aug 9, 2026, from https://www.medicare.gov/basics/get-started-with-medicare/sign-up/when-does-medicare-coverage-start
Using the GEP doesn't erase a late penalty. If you went without coverage during the months you could have had it, the penalty still attaches when you finally enroll. The GEP gets you in; it doesn't undo the cost of waiting.Centers for Medicare & Medicaid Services. (n.d.). When does Medicare coverage start?. medicare.gov. Retrieved Aug 9, 2026, from https://www.medicare.gov/basics/get-started-with-medicare/sign-up/when-does-medicare-coverage-start
Before you accept a penalty: seven more Special Enrollment Periods
Most guides stop at the working-past-65 window, so people who missed it assume the General Enrollment Period and a lifelong penalty are all that's left. That's wrong often enough to be worth checking. CMS lists seven further Special Enrollment Periods directly beneath the working-aged one, five of them added for "exceptional conditions" effective January 1, 2023.Centers for Medicare & Medicaid Services. (n.d.). When does Medicare coverage start?. medicare.gov. Retrieved Aug 9, 2026, from https://www.medicare.gov/basics/get-started-with-medicare/sign-up/when-does-medicare-coverage-start
| Special Enrollment Period | Who it's for | How long you have |
|---|---|---|
| Health plan or employer misrepresentation | You skipped enrolling because your employer, your group health plan, or their agent or broker told you something incorrect about Part B or premium Part A | Begins the day you notify Social Security, ends 6 months later |
| Emergency or disaster | A federal, state, or local government declared an emergency or disaster in your area | From the month of the emergency until 6 months after it ends |
| Termination of Medicaid | Your Medicaid ended on or after January 1, 2023 and you missed a Medicare window. Not available if you're still eligible, including through a Medicare Savings Program, and haven't had notice | From notice of the coming termination until 6 months after it |
| Formerly incarcerated | You didn't enroll because you were incarcerated | Your release date through the last day of the 12th month after release |
| Other exceptional conditions | Something beyond your control on or after January 1, 2023 made you miss a window and no other period fits. Granted only for genuinely exceptional situations, never forgetfulness or not knowing | Social Security sets the start case by case; runs at least 6 months |
| International volunteers | You were volunteering abroad at least 12 months for a tax-exempt organization and had insurance the whole time | 6 months, from whichever comes first: the service ending, the organization losing tax-exempt status, or that insurance ending |
| Certain TRICARE beneficiaries | You took Part A on disability or ESRD but skipped Part B because you had TRICARE Standard or TRICARE Prime | Not stated in the CMS listing; ask Social Security |
If one applies to you, start with the misrepresentation row. An employer or a benefits office telling someone they didn't need Part B is the single most common way a person misses this deadline, and this period exists for exactly that. It doesn't just postpone the penalty; it removes the wait and the penalty. You have to show two things, by documentation or written attestation: that you skipped an enrollment period you were eligible for based on what that employer, plan, agent, or broker told you, and that they materially misrepresented or gave incorrect information about signing up. Your six months run from the day you notify Social Security, and nothing starts that clock for you.Centers for Medicare & Medicaid Services. (n.d.). When does Medicare coverage start?. medicare.gov. Retrieved Aug 9, 2026, from https://www.medicare.gov/basics/get-started-with-medicare/sign-up/when-does-medicare-coverage-start
Two more things. Missing a Special Enrollment Period generally means you don't get another one, but the regulation carries an exception: under 42 CFR 406.24(d)(2), if you failed to enroll because your group health plan coverage was restored before that window closed, that failure doesn't preclude additional Special Enrollment Periods. And the forms differ by route: the five exceptional-conditions periods use CMS-10797, while the working-aged and working-disabled route uses CMS-18-F-5 (Parts A and B) or CMS-40B (Part B alone) plus the employer verification form CMS-L564. Our full guide to Medicare Special Enrollment Periods walks each one through.Centers for Medicare & Medicaid Services. (n.d.). When does Medicare coverage start?. medicare.gov. Retrieved Aug 9, 2026, from https://www.medicare.gov/basics/get-started-with-medicare/sign-up/when-does-medicare-coverage-start
Changing coverage later: the two "open enrollment" windows
Two more windows get lumped in with the others, but they do a different job. Neither is for signing up the first time; both change coverage you already have.
Fall Open Enrollment runs October 15 through December 7. During it, you can switch between Original Medicare and Medicare Advantage, join or change a Part D drug plan, or drop one for another. Any change you make takes effect January 1. This is the once-a-year window where most people review whether their current plan still fits, and it's worth using even if you don't expect to switch, because plans change their costs and drug lists from year to year.Centers for Medicare & Medicaid Services. (n.d.). Open Enrollment. medicare.gov. Retrieved Sep 2, 2026, from https://www.medicare.gov/health-drug-plans/open-enrollment
Medicare Advantage Open Enrollment runs January 1 through March 31. It's narrower: it's only for people already enrolled in a Medicare Advantage plan, and it allows one change. You can switch to a different Medicare Advantage plan, or drop back to Original Medicare and add a standalone Part D plan. If you're on Original Medicare, this window isn't for you.Centers for Medicare & Medicaid Services. (n.d.). Open Enrollment. medicare.gov. Retrieved Sep 2, 2026, from https://www.medicare.gov/health-drug-plans/open-enrollment
Neither of these lets a first-timer enroll in Medicare. If you've never signed up and you missed your IEP, the GEP above is your path, not these. One caution on names: plan changes after a life event such as moving or losing other insurance are also called Special Enrollment Periods. Those are windows to switch a Medicare Advantage or Part D plan. They are not the Part B window above, which turns on current-employment coverage only. Losing other coverage can move you between plans; it cannot get you into Part B.Centers for Medicare & Medicaid Services. (n.d.). Open Enrollment. medicare.gov. Retrieved Sep 2, 2026, from https://www.medicare.gov/health-drug-plans/open-enrollment
What a late penalty actually costs
This is the part that makes the windows matter. Sign up late without an exception that covers you and you don't just pay back-premiums, you pay a surcharge added to your premium that, for Part B and Part D, lasts as long as you have the coverage. Each part calculates it differently, and each part has its own escape: a Special Enrollment Period or a Medicare Savings Program for Part B, creditable drug coverage or Extra Help for Part D, and a Special Enrollment Period for Part A.Centers for Medicare & Medicaid Services. (n.d.). Avoid late enrollment penalties. medicare.gov. Retrieved Jul 15, 2026, from https://www.medicare.gov/basics/costs/medicare-costs/avoid-penalties
Part B. If you didn't sign up when first eligible and don't qualify for a Special Enrollment Period or a Medicare Savings Program, your monthly premium rises 10% for each full 12-month period you could have had Part B but didn't, and the penalty lasts as long as you have Part B. A two-year gap is a 20% surcharge, every month, for the rest of your life. Note what is not on that list: creditable drug coverage is the Part D test, not the Part B one.Centers for Medicare & Medicaid Services. (n.d.). Avoid late enrollment penalties. medicare.gov. Retrieved Jul 15, 2026, from https://www.medicare.gov/basics/costs/medicare-costs/avoid-penalties
Part D. For each full month you went without creditable drug coverage, Medicare adds 1% of the national base beneficiary premium to your Part D premium. The Part D late enrollment penalty is keyed to a national figure that changes each year, so your dollar penalty can shift slightly from year to year even though your percentage doesn't. It also lasts as long as you have Part D. Generally there is no Part D penalty if you had creditable drug coverage or you qualify for Extra Help.Centers for Medicare & Medicaid Services. (n.d.). Avoid late enrollment penalties. medicare.gov. Retrieved Jul 15, 2026, from https://www.medicare.gov/basics/costs/medicare-costs/avoid-penalties
Part A. Most people get Part A premium-free and never face this one. But if you have to buy Part A and you sign up late, your premium may go up 10%, and you pay that penalty for twice the number of years you delayed. Delay two years, pay the higher premium for four. Usually no penalty applies if you meet the conditions that let you sign up for Part A during a Special Enrollment Period.Centers for Medicare & Medicaid Services. (n.d.). Avoid late enrollment penalties. medicare.gov. Retrieved Jul 15, 2026, from https://www.medicare.gov/basics/costs/medicare-costs/avoid-penalties
The percentages stay abstract until you put a dollar on them, so here is the Part D math.
Worked example #1: a Part D late penalty
The figures below are Medicare's own published example, shown only to illustrate how the calculation works. They are not a real case and not a prediction of your own result.
Medicare works this one through itself. Say someone waited 14 full months after becoming eligible before joining a Part D plan, with no creditable drug coverage in between. Their penalty is 1% per month, so 14%. In 2026 the national base beneficiary premium that CMS sets for this calculation is $38.99. So the math is $38.99 × 0.14 = $5.46, which Medicare rounds to the nearest $0.10, landing at $5.50 a month. That gets added on top of whatever their chosen drug plan charges, and it sticks for as long as they keep Part D. The base figure is reset annually by CMS, so the exact dollar amount can drift year to year while the 14% stays fixed.Centers for Medicare & Medicaid Services. (2026). 2026 Medicare Part D Bid Information and Part D Premium Stabilization Demonstration Parameters. cms.gov. Retrieved Jul 10, 2026, from https://www.cms.gov/newsroom/fact-sheets/2026-medicare-part-d-bid-information-and-part-d-premium-stabilization-demonstration-parameters
$5.50 a month may not sound like much. But it never ends, and it grows with the delay: every extra uncovered month adds another 1%. Skip a few months of paperwork at 65 and you can be paying for it in your eighties.Centers for Medicare & Medicaid Services. (2026). 2026 Medicare Part D Bid Information and Part D Premium Stabilization Demonstration Parameters. cms.gov. Retrieved Jul 10, 2026, from https://www.cms.gov/newsroom/fact-sheets/2026-medicare-part-d-bid-information-and-part-d-premium-stabilization-demonstration-parameters
Frequently Asked Questions
When should I sign up for Medicare?
For most people, during their Initial Enrollment Period: the seven months around your 65th birthday. Sign up in the three months before your birthday month to have coverage ready the day you turn 65. The exception is if you're still working at 65 with coverage from a current employer, in which case you can usually delay and use a Special Enrollment Period later.Centers for Medicare & Medicaid Services. (n.d.). Open Enrollment. medicare.gov. Retrieved Sep 2, 2026, from https://www.medicare.gov/health-drug-plans/open-enrollment
Do I have to sign up for Medicare if I'm still working at 65?
Not necessarily. If you (or a spouse) are still working and you have health coverage from that current employer, you can usually delay Part B without a penalty and enroll later; the eight-month Special Enrollment Period runs for eight months from the month the job or that coverage ends. That window covers Part B and premium Part A, not Part D, whose own penalty starts once you go 63 days or more without creditable drug coverage. This Special Enrollment Period does not apply if you're eligible for Medicare based on End-Stage Renal Disease (ESRD). Confirm your employer's size and how its plan coordinates with Medicare before you decide to wait.Centers for Medicare & Medicaid Services. (n.d.). When does Medicare coverage start?. medicare.gov. Retrieved Aug 9, 2026, from https://www.medicare.gov/basics/get-started-with-medicare/sign-up/when-does-medicare-coverage-start
Does COBRA count as coverage that lets me delay Medicare?
No. COBRA and retiree coverage are not treated as current-employer coverage, so they do not let you delay Part B penalty-free and do not extend your Special Enrollment Period. Your eight-month window starts when your employment ends, not when COBRA runs out, so enroll in Part B around the time the job ends rather than waiting for COBRA to expire.Centers for Medicare & Medicaid Services. (n.d.). When does Medicare coverage start?. medicare.gov. Retrieved Aug 9, 2026, from https://www.medicare.gov/basics/get-started-with-medicare/sign-up/when-does-medicare-coverage-start
How long does the Medicare late enrollment penalty last?
For Part B and Part D, as long as you keep that coverage, meaning for life in most cases, but only if no exception covers you: there is no Part B penalty if you qualify for a Special Enrollment Period or a Medicare Savings Program, and generally no Part D penalty if you had creditable drug coverage or you qualify for Extra Help. The Part B penalty is 10% of the premium for each full year you delayed; the Part D penalty is 1% of the national base premium for each month you went without creditable drug coverage. The Part A penalty, which applies only if you buy Part A, lasts for twice the number of years you delayed.Centers for Medicare & Medicaid Services. (n.d.). Avoid late enrollment penalties. medicare.gov. Retrieved Jul 15, 2026, from https://www.medicare.gov/basics/costs/medicare-costs/avoid-penalties
What if I missed my Initial Enrollment Period?
Check the seven other Special Enrollment Periods first, especially if an employer or health plan told you that you didn't need Part B. That misrepresentation period runs six months from the day you notify Social Security and carries no penalty. Only if none of them fits do you sign up during the General Enrollment Period, January 1 through March 31. Coverage starts the first of the month after you enroll, and a late penalty may still apply for the time you went without.Centers for Medicare & Medicaid Services. (n.d.). When does Medicare coverage start?. medicare.gov. Retrieved Aug 9, 2026, from https://www.medicare.gov/basics/get-started-with-medicare/sign-up/when-does-medicare-coverage-start
Learn More
Find personalized help figuring out when to sign up for Medicare and which enrollment window fits your situation at brevy.com.
The information on Brevy.com is for educational purposes only and is not a substitute for professional legal, financial, or medical advice. Rules vary by state and program and change frequently. Always verify with the relevant agency or a qualified professional. Brevy is not a law firm, financial advisor, or healthcare provider.