You must enroll in Medicare during your Initial Enrollment Period, which starts three months before the month you turn 65 and ends three months after

Your Initial Enrollment Period is a seven-month window centered on your 65th birthday month. If you turn 65 in June, your period runs from March through September. You can enroll any time during those seven months, but the month you enroll determines when your coverage begins — enroll in April, coverage starts in June; enroll in June, coverage starts in August.

If you miss this window, you can still enroll later, but you will pay a permanent penalty on your premiums for as long as you have Medicare. The penalty is 10 percent of the standard Part B premium for each full 12 months you were not enrolled when you could have been. If you wait five years past your Initial Enrollment Period, you pay that 10 percent surcharge for life.

There are exceptions: if you were covered by an employer health plan while you or your spouse worked, or if you were a federal employee, you may have a Special Enrollment Period that lets you enroll without penalty up to eight months after that coverage ends. You must show proof of that employer coverage when you enroll.

Key Takeaways

  • Your Initial Enrollment Period is seven months long: three months before your 65th birthday month, the month itself, and three months after.
  • Enrolling during this window means no permanent penalty on your Part B or Part D premiums.
  • If you had employer health coverage while working, you may have until eight months after that coverage ends to enroll without penalty.
  • Every 12 months you delay past your Initial Enrollment Period adds 10 percent to your Part B premium for life.
  • You enroll through Medicare.gov, by phone at 1-800-MEDICARE, or in person at your local Social Security office.

What happens if you miss your Initial Enrollment Period

If you do not enroll during your seven-month window, you enter a General Enrollment Period that runs January 1 through March 31 each year. You can enroll then, but your coverage will not start until July 1 of that year. More importantly, you will owe a late enrollment penalty on Part B (medical insurance) and Part D (prescription drug coverage) for as long as you have Medicare.

The Part B penalty is 10 percent of the standard monthly premium for each 12-month period you were not enrolled. In 2024, the standard Part B premium is $164.90 per month; a 10 percent penalty adds $16.49 to your monthly bill permanently. If you wait two years, the penalty is 20 percent. The penalty does not go away when you turn 75 or after a certain number of years — it stays on your bill for life.

Part D (prescription drug) penalties work the same way. If you go 63 days or more without creditable drug coverage, you owe 1 percent of the national average Part D premium for each month you were without coverage. That penalty also lasts for life.

When you can enroll without penalty after 65

A Special Enrollment Period protects you if you had health coverage through an employer or union while you worked, or if you were a federal employee. When that coverage ends — whether because you retired, left the job, or the employer dropped the plan — you have eight months to enroll in Medicare without penalty. This is the only exception to the Initial Enrollment Period rule.

You must prove you had that coverage. Bring your insurance card, a letter from your employer's benefits office, or documentation from your union. Medicare will ask for this proof when you enroll. If you cannot show it, you will be treated as if you missed your Initial Enrollment Period and will owe the late penalty.

If your spouse was the one working and you were covered under their plan, the same eight-month window applies to you when their coverage ends. You do not have to wait until you turn 65 to use this period — you can enroll at any age if you are losing employer coverage.

How to enroll during your Initial Enrollment Period

You can enroll online at Medicare.gov by clicking "Sign up for Medicare" on the homepage. You will need your Social Security number, date of birth, and citizenship or immigration status. The online process takes about 10 minutes and you get confirmation when ready.

You can also call 1-800-MEDICARE (1-800-633-4227) and speak to a representative. They can answer questions about which parts of Medicare you need and walk you through enrollment over the phone. The line is open Monday through Friday, 8 a.m. to 8 p.m. Eastern time, and Saturday 9 a.m. to 1 p.m.

A third option is to visit your local Social Security office in person. Bring your Social Security card, proof of citizenship or legal residency, and proof of age. You can find your nearest office at ssa.gov. In-person enrollment takes longer than online or phone, but some people prefer it if they have questions or need help with paperwork.

Part A versus Part B enrollment timing

Part A (hospital insurance) and Part B (medical insurance) have different enrollment rules, though most people enroll in both during the same Initial Enrollment Period. Part A is usually free if you or your spouse paid Medicare taxes for at least 10 years while working. You are automatically enrolled in Part A when you turn 65 if you are already receiving Social Security benefits.

Part B requires a monthly premium and you must actively enroll — it is not automatic. If you delay Part B enrollment past your Initial Enrollment Period, you pay the 10 percent late penalty. However, if you were covered by an employer plan while working, you can delay Part B without penalty as long as that coverage continues. Once the coverage ends, you have eight months to enroll in Part B.

Part D (prescription drug coverage) also requires active enrollment and carries the same late penalty as Part B. If you go without creditable drug coverage for more than 63 days after your Initial Enrollment Period ends, the penalty applies. Some people delay Part D if they do not take many medications, but the penalty can add up quickly if they later need prescriptions.

Turning 65 while still working

If you are still working and covered by your employer's health plan when you turn 65, you can delay enrolling in Medicare Part B and Part D without penalty. Your employer coverage is considered creditable coverage, meaning it meets Medicare's standards. You have until eight months after you retire or lose that coverage to enroll without penalty.

You should still enroll in Part A during your Initial Enrollment Period, even if you delay Part B. Part A is usually free and has no monthly premium, so there is no cost to enrolling early. It covers hospital stays, skilled nursing care, and hospice.

When you do retire and lose employer coverage, contact Medicare right away. You have eight months from the date coverage ends to enroll in Part B and Part D. If you wait longer, the late penalty applies. Some employers send a notice when coverage will end; keep that letter because you will need to show it to Medicare as proof of when your coverage ended.

Medicare enrollment for people on disability or with ESRD

If you receive Social Security Disability Insurance (SSDI), you become may be able to access for Medicare automatically after you have been on disability for 24 months. You do not have to do anything — Medicare enrollment happens on its own. Your coverage begins on the 25th month of your disability.

If you have End-Stage Renal Disease (ESRD) — permanent kidney failure requiring dialysis or transplant — you are may be able to access for Medicare regardless of age. You have a different enrollment timeline: your Initial Enrollment Period is three months before the month dialysis or transplant is scheduled, the month itself, and three months after. If you miss this window, the same late penalties explore.

People with ESRD should enroll as soon as they know their treatment will begin, even if they are under 65. Waiting until after treatment starts can delay coverage and leave you responsible for medical bills.

Frequently Asked Questions

What if I turn 65 in the middle of a month?

Your birthday month counts as the center of your Initial Enrollment Period, regardless of the date. If you turn 65 on June 15, your seven-month window runs from March through September. You can enroll any time during those months.

Can I enroll in Medicare before I turn 65?

No, you cannot enroll before your 65th birthday. Your Initial Enrollment Period begins three months before the month you turn 65, so the earliest you can enroll is three months before that birthday month. If you turn 65 in September, you can start enrolling in June.

Do I have to enroll in Part D if I do not take many medications?

You are not required to enroll in Part D, but if you go without creditable drug coverage for more than 63 days, you will owe a late penalty when you do enroll. That penalty lasts for life. If there is any chance you might need prescriptions later, enrolling during your Initial Enrollment Period protects you from the penalty.

What if I am not a U.S. citizen?

You must be a U.S. citizen or a lawful permanent resident (green card holder) who has lived in the United States for at least five years to enroll in Medicare. If you are not yet a permanent resident, you cannot enroll until you are. Contact Medicare at 1-800-MEDICARE if you have questions about your immigration status and may be able to access.

Can I change my mind after I enroll?

Yes. You have until the end of the calendar year to make changes to your Medicare coverage during your Initial Enrollment Period. After that, you can make changes only during the annual Open Enrollment Period, which runs October 15 through December 7 each year, with changes taking effect January 1.