Quick answer: for most people, the best time to sign up for Medicare is during the three months before the month they turn 65. That is the start of the seven-month Initial Enrollment Period, and enrolling early in that window means Part B coverage begins on the first day of your birthday month. Signing up later in the window still works, but coverage starts the month after you enroll.
Medicare enrollment is built around a single date: your 65th birthday. Around that date sits a seven-month window called the Initial Enrollment Period (IEP). Use it well and coverage lines up neatly with the end of other insurance. Miss it without a qualifying reason, and you may wait months for coverage and pay a higher Part B premium for as long as you have it.
This article explains the IEP in detail: how to count the months, when coverage starts depending on the month you sign up, who gets enrolled automatically, special cases such as birthdays on the first of the month and disability-based eligibility, and what to do if you are still working. It is one of the deeper guides in our complete Medicare guide, which covers costs, plan choices and every enrollment window in one place. For a refresher on what each part covers, see Medicare Parts A, B, C and D explained.
Timing rules below come from Medicare.gov’s page on when Medicare coverage starts and the Social Security Administration, checked October 2026. This is general information, not advice for your personal situation.
How the Initial Enrollment Period Works
The IEP lasts seven months. It begins three months before the month you turn 65, includes your birthday month, and ends three months after your birthday month. During those months you can sign up for Part A, Part B or both, and you can join a Medicare Advantage plan or a Part D drug plan.
Counting the months
Take someone whose 65th birthday falls on June 15. Their window runs like this:
- March: first month of the IEP
- April: second month
- May: third month
- June: birthday month
- July: fifth month
- August: sixth month
- September: seventh and final month
The window opens on the first day of March and closes on the last day of September. The exact day of the birthday inside June does not change the window, with one exception covered below.
Why the window is seven months
A seven-month span gives people time to plan around retirement dates, employer coverage and other insurance. It also gives Social Security time to process applications. Starting early avoids gaps, while the months after the birthday act as a safety margin for anyone who needs it.
When Your Coverage Starts
The month you sign up decides when your coverage begins, and Medicare coverage always starts on the first of a month.
| If you sign up for Part B | Coverage starts |
|---|---|
| In any of the 3 months before your birthday month | The first day of your birthday month |
| In your birthday month | The first day of the next month |
| In any of the 3 months after your birthday month | The first day of the month after you sign up |
Premium-free Part A works a little differently. Medicare.gov says Part A coverage starts in the month you turn 65 for people who qualify for premium-free Part A. If you sign up for premium-free Part A after you turn 65, coverage can reach back up to six months, though never earlier than the month you turned 65.
What this means in practice
Using the June birthday example, signing up in March, April or May gives Part B coverage starting June 1. Signing up in June starts coverage July 1. Signing up in August starts coverage September 1. Anyone ending employer coverage, Marketplace coverage or COBRA around their birthday should aim for the early months so that the old coverage and Medicare overlap or meet with no gap.
Older rules once delayed coverage by up to three months for people who signed up late in the window. Since January 2023, coverage begins the month after enrollment for sign-ups during or after the birthday month, which shortens any gap but does not remove it.
Are You Enrolled Automatically?
Some people never have to apply for Parts A and B.
Automatic enrollment. If you already receive Social Security or Railroad Retirement Board benefits at least four months before you turn 65, you are usually enrolled in Parts A and B automatically. Your Medicare card arrives in the mail about three months before your birthday. Part B is optional, and the card package explains how to decline it if you have other qualifying coverage, such as job-based insurance through current employment.
Manual sign-up. If you are not yet collecting Social Security, you must sign up yourself. This group is growing because full retirement age for Social Security is now 67 for people born in 1960 or later, while Medicare eligibility still starts at 65. Many people therefore reach 65 before they claim retirement benefits and need to enroll on their own.
How to sign up
Medicare.gov’s page on how to sign up for Medicare lists three routes through the Social Security Administration:
- Apply online at SSA.gov, which is usually the fastest way.
- Call Social Security at 1-800-772-1213 (TTY 1-800-325-0778).
- Visit a local Social Security office, ideally with an appointment.
People who worked for a railroad should contact the Railroad Retirement Board instead. Keep the confirmation number or receipt from your application in case questions come up.
Special Situations That Change the Timing
Several situations shift the window or replace it with a different one.
Your birthday is on the first of the month
Medicare and Social Security treat people born on the first of a month as turning 65 in the previous month. So someone born on June 1 has an IEP that starts in February and ends in August, and premium-free Part A coverage begins May 1. If your birthday is on the first, count your window from the month before.
You qualify through disability
People under 65 who receive Social Security disability benefits are enrolled in Parts A and B automatically after 24 months of benefits. The IEP for these beneficiaries is built around the 25th month of disability benefits, with the same three-months-before and three-months-after structure. Our guide to disability insurance basics explains how private disability coverage differs from Social Security disability.
You have ALS or end-stage renal disease
People with ALS get Medicare automatically the month their disability benefits begin. End-stage renal disease follows separate rules tied to dialysis and transplant timing, and Medicare.gov notes that the job-based Special Enrollment Period does not apply to people eligible because of ESRD.
You live in Puerto Rico
People in Puerto Rico who receive Social Security benefits are enrolled in Part A automatically, but they must sign up for Part B themselves.
Still Working at 65? Your Options
The IEP applies to everyone, but people with job-based health coverage may not need Part B right away.
Medicare.gov explains that if you or your spouse are still working and have group health coverage through that current job, you can usually delay Part B and sign up later without a penalty. That later chance is a Special Enrollment Period, and it lasts for eight months after the job or the group coverage ends, whichever comes first. If you sign up while still working, or within the first full month after employer coverage ends, you can ask to delay your Part B start date by up to three months.
A few details matter here:
- Employer size changes how coverage works. With 20 or more employees, the group plan usually pays first. With fewer, Medicare often pays first, and the plan may expect you to have Part B.
- COBRA and retiree coverage are not based on current employment. Medicare.gov is clear that getting COBRA does not extend the eight-month window.
- Marketplace coverage does not qualify for the job-based Special Enrollment Period. Our explainer on open enrollment and special enrollment periods covers how Marketplace windows work for younger family members.
- Many people take premium-free Part A at 65 even while working, because it has no premium. Anyone contributing to a health savings account should check the HSA rules first, since enrolling in any part of Medicare ends eligibility to contribute.
Ask your employer’s benefits office, in writing, how its plan coordinates with Medicare. Their answer decides whether delaying Part B makes sense for you.
What Happens If You Miss Your Initial Enrollment Period
Missing the IEP is fixable, but it can be costly.
The General Enrollment Period
People who miss the IEP and do not qualify for a Special Enrollment Period can sign up during the General Enrollment Period, January 1 to March 31 each year. Coverage starts the month after you sign up. Depending on when the IEP ended, that can still leave months without coverage.
The Part B penalty
According to Medicare.gov, the Part B late enrollment penalty adds 10% to the monthly premium for each full 12-month period you could have had Part B but went without it and without qualifying coverage. The penalty generally lasts as long as you have Part B. With the standard 2026 premium at $202.90 a month, the penalty is calculated on that amount and changes as the premium changes each year.
The Part D penalty
Drug coverage has its own penalty. If you go 63 days or more in a row after your IEP without Part D or other creditable drug coverage, a penalty is added to your Part D premium for as long as you have drug coverage.
Exceptional situations
Since 2023, Medicare has offered Special Enrollment Periods for some exceptional situations, such as losing Medicaid coverage, being affected by a declared disaster or emergency, receiving incorrect information from an employer or health plan, or release from incarceration. These are requested through Social Security using form CMS-10797, as described on Medicare.gov’s page on special enrollment periods.
A Simple Sign-Up Timeline
Planning works best when it starts well before your birthday. Here is a straightforward timeline built on the IEP rules above.
- Six months before your birthday month: Confirm whether you will be enrolled automatically. Gather information about your current coverage and, if you are working, ask your employer how its plan works with Medicare.
- Four months before: Compare Original Medicare with Medigap against Medicare Advantage, and list your prescriptions for a Part D comparison in the Medicare Plan Finder.
- Three months before (IEP opens): Apply for Parts A and B through Social Security if you are not enrolled automatically.
- Two months before: Choose and join a Part D plan or a Medicare Advantage plan, so coverage starts with Medicare.
- Birthday month: Confirm your Medicare card has arrived and that any new plan has sent a welcome packet and member card. If you bought Medigap, note that your six-month Medigap Open Enrollment Period started with Part B.
- After the birthday: Cancel older coverage only once Medicare and any new plan are confirmed active.
Free, unbiased counseling is available from your State Health Insurance Assistance Program (SHIP) at every step.
FAQ
Frequently Asked Questions
Can I sign up for Medicare before I turn 65?
Yes. Your Initial Enrollment Period starts three months before the month you turn 65, and signing up then means Part B coverage begins on the first day of your birthday month.
What if my birthday is on the first of the month?
Medicare treats you as turning 65 in the previous month, so your window and coverage start one month earlier than they otherwise would.
Do I need to sign up for Medicare if I already get Social Security?
Usually not. People who receive Social Security benefits at least four months before turning 65 are generally enrolled in Parts A and B automatically and receive their card in the mail.
Can I sign up for Part A and delay Part B?
Yes. Many people with job-based coverage from current employment take premium-free Part A and delay Part B, then use the Special Enrollment Period later. Check HSA rules first, because any Medicare enrollment ends HSA contribution eligibility.
What happens if I miss the Initial Enrollment Period?
You can usually sign up during the General Enrollment Period from January 1 to March 31, with coverage starting the month after you enroll. A late enrollment penalty may apply unless you qualify for a Special Enrollment Period. N: This article is general information only and is not insurance, legal or tax advice. Rules and amounts were checked on Medicare.gov and with the Social Security Administration in October 2026. For help with your situation, contact Social Security, 1-800-MEDICARE or your State Health Insurance Assistance Program.
