You enroll in Medicare at 65, but the exact month depends on your birthday and whether you are still working

Medicare enrollment opens three months before the month you turn 65 and closes three months after. If your birthday is in June, for example, enrollment runs from March through September. You do not have to enroll the moment it opens — you can wait until the month you turn 65 itself, or even delay if you meet certain conditions. But missing the window without a valid reason triggers a permanent penalty on your Part B and Part D premiums.

The main exception: if you are still working and covered by your employer's health plan, you can delay enrollment without penalty as long as the employer has 20 or more employees. Once you or your spouse stops working, you have eight months from the end of that coverage to enroll without penalty. This is called a Special Enrollment Period.

Social Security handles Medicare enrollment automatically for most people. If you are already receiving Social Security benefits before 65, Medicare starts the month you turn 65 with no action needed. If you are not yet receiving Social Security, you must contact Social Security or Medicare directly during your enrollment window.

Key Takeaways

  • Medicare enrollment opens three months before you turn 65 and closes three months after, with the important date tied to your birthday month, not a fixed calendar date.
  • If you are still working and have employer coverage with 20 or more employees, you can delay enrollment without penalty until eight months after you leave that job.
  • Missing your enrollment window without a may have access to reason results in a permanent 10 percent increase to your Part B premium for each year you were late, and similar penalties for Part D.
  • Social Security enrolls you automatically in Medicare Part A and Part B if you are already receiving benefits; if not, you must contact Social Security or Medicare yourself.
  • Your enrollment window is personal to your birthday — it does not reset each calendar year, so waiting too long in your window means waiting until the next year to enroll.

How the three-month enrollment window works

Your Initial Enrollment Period is seven months long: three months before the month you turn 65, the month you turn 65, and three months after. Within that window, you can enroll in Part A (hospital insurance) and Part B (medical insurance) without penalty, regardless of when in the window you sign up.

The window is tied to your birthday month, not to the calendar year. If you turn 65 in September, your window runs from June through December. If you turn 65 in January, your window runs from October of the previous year through April. Once your window closes, you cannot enroll in Part B until the next General Enrollment Period, which runs January 1 through March 31 each year — but by then you will owe back premiums and face the late-enrollment penalty.

You do not have to enroll on the first day your window opens. Many people wait until the month they actually turn 65, or even until the last month of their window. The risk is forgetting the important date entirely. Mark your calendar for the last month of your window as a reminder.

When you can delay enrollment without a penalty

The main reason to delay is employer coverage. If you or your spouse is still working and your employer's health plan covers you, you can delay Part B enrollment without penalty. This applies only if the employer has 20 or more employees. Small employers do not count — if your employer has fewer than 20 people, you should enroll in Medicare at 65 even if you have coverage through them.

Once you or your spouse stops working, or the employer coverage ends for any reason, you have eight months to enroll in Part B without penalty. This eight-month window is separate from your Initial Enrollment Period. If your Initial Enrollment Period has already passed, the eight-month Special Enrollment Period is your second chance. You must contact Social Security or Medicare directly to use this period — it does not happen automatically.

Part A (hospital insurance) has different rules. If you have employer coverage, you can delay Part A enrollment without penalty only if you are still actively working. Once you stop working, you should enroll in Part A even if you delay Part B. Part A has no premium for most people, so there is no financial reason to wait.

What happens if you miss your enrollment important date

Missing your Initial Enrollment Period without a may have access to reason results in a late-enrollment penalty on Part B. The penalty is 10 percent of the standard Part B premium for each full year you were may be able to access but not enrolled. If you were may be able to access for three years before enrolling, you pay 30 percent more than the standard premium — and you pay this extra amount for as long as you have Part B. The penalty does not go away.

Part D (prescription drug coverage) has a similar penalty: 1 percent of the national average Part D premium for each month you were may be able to access but not enrolled. If you go 24 months without Part D coverage, the penalty is 24 percent of that average, and again, it is permanent.

The only way to avoid these penalties is to enroll during your Initial Enrollment Period, use a Special Enrollment Period if you may have access to, or wait until the next General Enrollment Period (January through March) if you miss your window. But enrolling in a later General Enrollment Period means paying the penalty retroactively.

Automatic enrollment through Social Security

If you are already receiving Social Security retirement, disability, or survivor benefits before you turn 65, Medicare Part A and Part B start automatically the month you turn 65. You do not have to do anything. Social Security sends you a Medicare card in the mail about two weeks before your coverage begins.

If you are not yet receiving Social Security when you turn 65, you must contact Social Security or Medicare to enroll. You can call Social Security at 1-800-772-1213, visit your local Social Security office, or go online to ssa.gov. You can also call Medicare directly at 1-800-MEDICARE (1-800-633-4227) or visit Medicare.gov. Whichever route you choose, have your Social Security number and birth certificate ready.

Even if you delay Part B enrollment because of employer coverage, you should still enroll in Part A at 65 if you are not automatically enrolled. Part A is free for most people and covers hospital stays. There is no reason to wait.

Special cases: working past 65 and government employees

If you are self-employed or own a business, you are not covered by the employer-coverage exception. You should enroll in Medicare at 65 even if your business is still operating and you are still working. The exception applies only to employees of employers with 20 or more workers.

Federal employees and railroad workers have their own retirement systems and may have different Medicare rules. If you worked for the federal government or a railroad, contact your agency's benefits office or the Railroad Retirement Board before your 65th birthday to understand how your coverage works with Medicare.

If you are still working past 65 and have employer coverage, you can delay Part B, but you must still enroll in Part A at 65. Some people choose to delay both, but this is usually a mistake because Part A is free and covers hospital care that employer plans may not fully cover.

How to enroll when your window opens

You have three ways to enroll: online, by phone, or in person. The fastest is online at Medicare.gov. Go to the "Sign Up for Medicare" section, create an account or log in, and follow the steps. You will need your Social Security number and birth certificate. Enrollment usually takes 10 to 15 minutes.

By phone, call Medicare at 1-800-MEDICARE (1-800-633-4227). Representatives are available Monday through Friday, 8 a.m. to 8 p.m. Eastern time. Have your Social Security number, birth certificate, and information about any current health coverage ready. The call usually takes 20 to 30 minutes.

In person, visit your local Social Security office. Bring your Social Security card, birth certificate, and proof of citizenship (passport, naturalization certificate, or birth certificate). You can find your local office at ssa.gov or call 1-800-772-1213 to make an appointment. Walk-ins are accepted but waits can be long.

Frequently Asked Questions

Can I enroll in Medicare before I turn 65?

No. Enrollment opens three months before the month you turn 65, not before. If your birthday is in June, enrollment opens in March. You cannot enroll in February even if you are turning 65 in June.

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

Your enrollment window is based on the month you turn 65, not the specific date. If you turn 65 on June 15 or June 1, your window is the same: March through September. Your coverage starts on the first day of the month you turn 65.

Do I have to enroll in Part B if I enroll in Part A?

No. Part A and Part B are separate. You can enroll in Part A without Part B if you have other coverage. But if you delay Part B past your Initial Enrollment Period without a may have access to reason, you will owe the late-enrollment penalty when you do enroll.

What if I am still working at 65 but my employer does not offer health insurance?

You should enroll in Medicare at 65. The employer-coverage exception applies only if your employer actually provides a health plan. If your employer does not offer coverage, you have no reason to delay.

Can I change my mind after I enroll?

Yes. You have a seven-day window after you enroll to cancel and restart your enrollment if you made a mistake. After seven days, you can make changes only during the General Enrollment Period (January through March) or if you have a may have access to life event like losing employer coverage.