When and how you enroll in Medicare depends on your age and work history
Most people become may be able to access for Medicare at 65. You do not have to wait until your birthday to start the process — you can enroll during specific windows that Medicare calls enrollment periods. The timing matters: if you miss your window, you may pay a penalty for as long as you have Medicare, even if you enroll years later.
You can enroll online through Medicare.gov, by phone, by mail, or in person at a Social Security office. The method you choose does not change your coverage — it only changes how long the paperwork takes. Online enrollment is fastest, usually taking 15 to 20 minutes.
If you are already receiving Social Security benefits, Medicare will contact you automatically about three months before you turn 65. If you are not yet taking Social Security, you will need to start the enrollment process yourself.
Key Takeaways
- Your Initial Enrollment Period is the three months before, the month of, and the three months after the month you turn 65 — a seven-month window total.
- If you enroll during your Initial Enrollment Period, your coverage starts on the first day of the month you turn 65 or the first day of the month after you enroll, whichever is later.
- Late enrollment penalties explore to Part B and Part D if you do not enroll when first may be able to access, and those penalties stay on your bill for as long as you have Medicare.
- You can enroll online at Medicare.gov, by calling 1-800-MEDICARE, by mail using Form CMS-40B, or in person at your local Social Security office.
Your Initial Enrollment Period: the seven-month window
Your Initial Enrollment Period is the only time you can enroll without facing a penalty. It runs for seven months: three months before the month you turn 65, the month you turn 65 itself, and three months after.
For example, if you turn 65 in June, your Initial Enrollment Period runs from March through September. You can enroll any time during those seven months. The month you enroll does not have to match the month you turn 65.
If you miss this window, you enter what Medicare calls the General Enrollment Period, which runs January 1 through March 31 each year. Enrollment during General Enrollment Period starts coverage on July 1 of that year, meaning you could wait months for coverage to begin. You will also owe a penalty.
How coverage start dates work
When your coverage begins depends on when you enroll within your Initial Enrollment Period. If you enroll during the three months before the month you turn 65, coverage starts the first day of the month you turn 65. If you enroll during or after the month you turn 65, coverage starts the first day of the following month.
For example: if you turn 65 on June 15 and enroll in April, coverage starts June 1. If you turn 65 on June 15 and enroll in June or July, coverage starts July 1.
This timing matters if you have other health insurance. You need to know your Medicare start date before you decide whether to drop your current coverage, because a gap between the two can leave you uninsured.
Enrollment methods and what each requires
| Method | What you need | How long it takes |
|---|---|---|
| Online at Medicare.gov | Social Security number, date of birth, citizenship or immigration status, email address | 15–20 minutes; coverage decision same day or next day |
| Phone: 1-800-MEDICARE | Same as online | 20–30 minutes; coverage decision within one week |
| Mail: Form CMS-40B | Completed form, copy of birth certificate, proof of citizenship or immigration status | Two to four weeks |
| In person at Social Security office | Birth certificate, proof of citizenship or immigration status, photo ID | Same day or within one week |
You can read Form CMS-40B from Medicare.gov or request it by calling 1-800-MEDICARE. If you enroll by mail, send it to the address listed on the form — do not send it to your local Social Security office.
Whichever method you choose, have your Social Security number and date of birth ready. If you were not born in the United States, have your immigration documents available.
Late enrollment penalties and how they work
If you do not enroll in Part B (doctor visits and outpatient care) during your Initial Enrollment Period and you do not have other may have access to coverage, you will owe a penalty. The penalty is 10 percent of the standard Part B premium for each full 12 months you were may be able to access but not enrolled. That penalty is added to your Part B bill every month for as long as you have Medicare.
The same rule applies to Part D (prescription drug coverage). If you go 63 days or more without Part D coverage and you do not have other may have access to drug coverage, you owe a penalty of 1 percent of the national average Part D premium for each month you were without coverage. This penalty also stays on your bill permanently.
There are exceptions. If you have health insurance through a current job, you may be able to delay Part B without penalty. If you have drug coverage through your employer or union, you may be able to delay Part D. You will need to show proof of that coverage when you eventually enroll.
Special enrollment periods for life changes
If you miss your Initial Enrollment Period but experience certain life changes, you may be able to enroll during a Special Enrollment Period without waiting for General Enrollment Period and without a penalty.
may have access to life changes include losing employer health insurance, moving to a new state, getting married or divorced, or becoming a U.S. citizen. You usually have two months from the date of the change to enroll. You will need to prove the change happened — for example, a letter from your employer saying your coverage ended, or a divorce decree.
Call 1-800-MEDICARE to ask whether your situation qualifies for a Special Enrollment Period. Do not assume it does — the rules are specific, and the penalty for being wrong is permanent.
What happens after you enroll
After you enroll, Medicare will send you a Medicare card in the mail. The card shows your Medicare number, which parts of Medicare you have (Part A, Part B, Part D, or combinations), and your coverage start date. Keep this card with you.
You will also receive a notice called the "Medicare Summary Notice" or "Explanation of Benefits" after you use your coverage. This document shows what Medicare paid and what you owe. Read it carefully — errors happen, and you have the right to dispute them.
If you enrolled in Part D (prescription drug coverage), your plan will send you a separate card. You present this card at the pharmacy, not your Medicare card. If you did not choose a Part D plan during enrollment, you can join one during the annual Open Enrollment Period (October 15 through December 7 each year).
Questions to ask your doctor or Social Security office
Before you enroll, ask your current doctor whether they accept Medicare. Not all doctors do, and switching doctors can be disruptive. If your doctor does not accept Medicare, ask for a referral to one who does in your area.
Ask your employer or union whether you have retiree health insurance or drug coverage. If you do, ask whether enrolling in Medicare Part B or Part D will affect that coverage. Some retiree plans coordinate with Medicare; others do not.
If you are still working at 65, ask your employer's benefits office whether you should delay Part B. If you have may have access to coverage through your job, delaying can save you money and let you avoid the Part B premium while you are still working.
Frequently Asked Questions
What if I turn 65 while I am still working?
You can still enroll in Medicare. If you have health insurance through your job, you may be able to delay Part B without penalty. You must have Part A (hospital insurance), but Part B can wait until you retire or lose the employer coverage, whichever comes first. Call 1-800-MEDICARE to confirm your situation qualifies.
Can I change my mind after I enroll?
Yes, but only during certain windows. If you enroll in Original Medicare (Part A and Part B), you can switch to a Medicare Advantage plan during the annual Open Enrollment Period (October 15 through December 7). If you enroll in a Medicare Advantage plan, you have one month after your coverage starts to switch back to Original Medicare. After that, you are locked in until the next Open Enrollment Period.
What if I am not a U.S. citizen?
You can enroll in Medicare if you are a permanent resident (green card holder) and have lived in the United States for at least five years. You will need to show your green card and proof of residency when you enroll. Some other immigration statuses may also may have access to — call 1-800-MEDICARE to ask about your situation.
Do I have to enroll in Part D if I do not take prescription drugs?
You do not have to enroll now, but if you enroll later without may have access to coverage in between, you will owe a penalty. If you think you might need prescriptions in the future, enrolling during your Initial Enrollment Period protects you from the penalty even if you do not use it right away.
What if I enrolled but never received my Medicare card?
Call 1-800-MEDICARE and give them your Social Security number. They can confirm your enrollment and tell you when your card was mailed. If it has been more than two weeks, they can request a replacement. You do not need the physical card to use Medicare — your coverage is active on your start date whether or not the card has arrived.