When Medicare Begins

Medicare coverage starts on the first day of the month you turn 65, or the first day of the month you become may be able to access due to disability or end-stage renal disease. If your birthday falls on the first of the month, coverage begins that day. If your birthday is any other day, coverage begins the first of the following month.

You do not have to wait for a card to arrive in the mail to use your coverage. Your benefits are active on your start date even if you have not received your physical Medicare card yet. You can use your Social Security number as your Medicare number at the doctor's office or hospital until the card arrives, which typically takes two to four weeks after your coverage begins.

The timing of when you sign up for Medicare affects when coverage starts and whether you face late-enrollment penalties. If you sign up during your initial enrollment period — the seven-month window that includes the month you turn 65 and the three months before and after — coverage begins the month you turn 65 with no penalty. If you miss this window, your coverage start date shifts based on when you eventually sign up, and you may owe a permanent increase to your premiums.

Key Takeaways

  • Medicare coverage begins the first day of the month you turn 65, regardless of when you sign up, unless you miss your initial enrollment period.
  • You do not need your physical Medicare card to start using benefits; your Social Security number works at providers until the card arrives.
  • Signing up late — after your initial enrollment period ends — delays your coverage start date and triggers permanent premium penalties.
  • If you are still working and covered by employer health insurance at 65, you may be able to delay Medicare Part B without penalty, but you must sign up for Part A.
  • Your existing health insurance does not automatically end when Medicare starts; you must cancel it yourself or it will overlap and charge you twice.

Your Initial Enrollment Period and Why It Matters

Your initial enrollment period is a seven-month window: three months before the month you turn 65, the month you turn 65, and three months after. During this window, you can sign up for Medicare Part A (hospital insurance) and Part B (medical insurance) without waiting or facing penalties.

If you sign up during this period, your Part A coverage starts the first of the month you turn 65. Part B coverage also starts that month if you sign up before your birthday or during your birthday month. If you sign up in the three months after your birthday month, Part B coverage is delayed by one month for each month you wait — so signing up one month late means Part B starts two months after your 65th birthday.

Missing your initial enrollment period means you cannot sign up again until the next general enrollment period, which runs January 1 through March 31 each year. Coverage would not start until July 1 of that year. During the gap, you have no Medicare coverage unless you are covered by an employer plan or another source.

What Happens to Your Current Health Insurance

When Medicare starts, your existing health insurance — whether through an employer, a spouse's employer, or a private plan you bought yourself — does not stop automatically. You must cancel it yourself, or both plans will remain active and you will receive bills from both.

If you have employer coverage through your own job or your spouse's job, contact the human resources or benefits department and tell them your Medicare start date. They will tell you the important date to notify them and what happens to your coverage. Some employers end coverage automatically when you become Medicare-may be able to access; others require you to opt out. If you have a private plan you purchased yourself, call the insurance company or log into your account and request cancellation effective your Medicare start date.

Coordinating the end of your old plan with the start of Medicare prevents gaps and overlaps. A gap means you have no coverage for a period. An overlap means you are paying premiums to two insurers for the same coverage period, and claims may be denied because Medicare and your old plan argue over who pays first.

Late Enrollment Penalties and How They Work

If you do not sign up for Medicare Part B during your initial enrollment period and you do not have other may have access to coverage, you will owe a late enrollment penalty for as long as you have Part B. The penalty is a percentage of the Part B premium amount at the time you sign up, multiplied by the number of months you were late. This penalty is permanent — it does not go away after a certain time.

Part A does not usually carry a late enrollment penalty if you have worked long enough to may have access to for it based on your own or your spouse's work history. However, if you do not have enough work credits, you may have to pay a premium for Part A, and that premium increases if you sign up late.

You can avoid the late enrollment penalty if you have creditable coverage — health insurance through an employer, a spouse's employer, TRICARE, the Veterans Health Administration, or certain other sources — at the time you become may be able to access for Medicare. If you have creditable coverage, you can delay signing up for Part B without penalty, as long as you sign up within eight months of losing that coverage. You must still sign up for Part A at 65.

Signing Up Before Your Coverage Starts

You should sign up for Medicare during your initial enrollment period, which means signing up before your 65th birthday or shortly after. The Social Security Administration, Medicare.gov, and your local Social Security office all handle sign-ups.

Online sign-up through Medicare.gov is available 24 hours a day. You will need your Social Security number, date of birth, and information about any current health coverage. The process takes about 15 minutes. You can also call Social Security at 1-800-772-1213 (TTY 1-800-325-0778) to sign up by phone, or visit your local Social Security office in person.

After you sign up, Social Security sends a confirmation letter and your Medicare card. The card typically arrives within two to four weeks. If you need coverage to start and your card has not arrived, you can use your Social Security number as your Medicare number at any provider.

What to Do If You Miss Your Initial Enrollment Period

If you miss your initial enrollment period and you do not have creditable coverage, you have two options: wait for the next general enrollment period or look for a special enrollment period.

The general enrollment period runs January 1 through March 31 each year. You can sign up during this window, but coverage does not start until July 1. This means if you miss your initial enrollment period in, say, August, you cannot get coverage until the following July — nearly a year later. During that gap, you have no Medicare coverage.

A special enrollment period allows you to sign up outside the normal windows if you have a may have access to event — such as losing employer coverage, moving to a new state, or having a change in your immigration status. If you think you may have access to for a special enrollment period, contact Social Security or Medicare to ask. The rules are strict, and not all life changes may have access to.

Coordinating Medicare with Employer Coverage

If you are still working at 65 and covered by your employer's health plan, you may be able to delay Medicare Part B without penalty. However, the rules depend on the size of your employer and whether you are the employee or the spouse of an employee.

If you work for an employer with 20 or more employees and you are covered by the employer plan, you can delay Part B. You must still sign up for Part A at 65. When you eventually leave your job or lose the employer coverage, you have eight months to sign up for Part B without penalty.

If your employer has fewer than 20 employees, Medicare becomes your primary payer at 65, even if you are still working and covered by the employer plan. In this case, you should sign up for both Part A and Part B at 65 to avoid penalties and gaps in coverage.

If you are covered by your spouse's employer plan, the same rules explore based on your spouse's employer size, not your own employment status. Discuss your situation with your employer's benefits department or call Medicare at 1-800-633-4227 to confirm what applies to you.

Frequently Asked Questions

What if I turn 65 on the first day of the month?

Your Medicare coverage starts that same day. You do not have to wait until the next month. Your initial enrollment period still runs three months before, the month of, and three months after your birthday.

Can I use Medicare before my card arrives?

Yes. Your coverage is active on your start date. Use your Social Security number as your Medicare number when you see a doctor or go to the hospital. Providers can look up your coverage using your Social Security number and date of birth.

What happens if I sign up for Medicare but do not cancel my old insurance?

Both plans remain active and you will receive bills from both. You must contact your old insurance company or employer benefits department and request cancellation. Coordinate the cancellation date with your Medicare start date to avoid gaps or overlaps.

Do I have to sign up for Part B if I am still working?

You must sign up for Part A at 65. Part B is optional if you have employer coverage through your own job or your spouse's job at an employer with 20 or more employees. If your employer has fewer than 20 employees, you should sign up for Part B to avoid penalties.

What is the late enrollment penalty for Part B?

The penalty is 10 percent of the Part B premium for each full year you were late. This penalty is permanent and added to your premium for life. For example, if you are three years late and the Part B premium is $165, your penalty would be 30 percent of $165, or about $50 per month, added to your premium forever.