Medicare coverage start dates depend on when you sign up and which enrollment period you’re using. Signing up on time is important to avoid delays and potential penalties.

Initial Enrollment Period (IEP)

Your first opportunity to sign up for Medicare is called your Initial Enrollment Period. It lasts 7 months:

  • Begins 3 months before the month you turn 65

  • Includes your birthday month

  • Ends 3 months after your birthday month

If you sign up before the month you turn 65, your coverage usually starts the month you turn 65.
If you sign up during or after your birthday month, coverage will start the following month.

Watch this short video from CMS to learn more:

Coverage Start Dates for Premium-Free Part A

If you qualify for premium-free Part A (usually by working and paying Medicare taxes for 10 years), your Part A coverage begins:

  • The month you turn 65

  • Or, the month before you turn 65 if your birthday is on the 1st of the month

You can also sign up for Part A after age 65, and coverage can be retroactive for up to 6 months, but it can’t start earlier than the month you turned 65.

Coverage Start Dates for Part B and Premium-Part A

If you sign up for Part B (or Premium-Part A):

If you sign up… Coverage starts…
Before your 65th birthday month The month you turn 65
During your birthday month or the 3 months after The next month
Avoiding Late Enrollment Penalties

If you don’t sign up for Part B during your Initial Enrollment Period and don’t qualify for a Special Enrollment Period, you may pay a late enrollment penalty. This penalty is 10% for each full 12-month period you could have had Part B but didn’t—and it lasts as long as you have Part B.

Special Enrollment Periods (SEPs)

You may qualify for a Special Enrollment Period if certain life events delayed your enrollment. Examples include:

  • Losing Medicaid coverage

  • Having or losing job-based coverage

  • Being impacted by a disaster or emergency

  • Receiving incorrect info from an employer or health plan

  • Recently being released from incarceration

  • Serving as a volunteer outside the U.S.

  • Having TRICARE coverage

Coverage during a Special Enrollment Period generally starts the month after you sign up, though in some cases you may choose an earlier or later start date. You’ll typically need to complete Form CMS-10797 and send it to your local Social Security office.

General Enrollment Period

If you miss both your Initial and any Special Enrollment Period, you can enroll during the General Enrollment Period:

  • January 1 to March 31 each year

  • Coverage begins the month after you sign up

  • You may have to pay late enrollment penalties

A Note About HSAs (Health Savings Accounts)

If you have an HSA with a High Deductible Health Plan, you should stop contributing to your HSA at least 6 months before you apply for Medicare. That’s because:

  • Part A coverage can start up to 6 months retroactively

  • You’re not allowed to contribute to an HSA while enrolled in any part of Medicare

  • If your Medicare Part A overlaps with HSA contributions, you may face tax penalties

You can continue to use HSA funds to pay for Medicare-related expenses like premiums, deductibles, and copayments—even after Medicare begins.