Most people can first sign up during their Initial Enrollment Period, a 7-month window. It starts 3 months before the month you turn 65 and ends 3 months after.
What matters most
A 7-month window
Your Initial Enrollment Period (the first time you can sign up) lasts 7 months. It starts 3 months before the month you turn 65 and ends 3 months after.
Sign up early for on-time coverage
If you sign up in the 3 months before your birthday month, your coverage can start the first day of the month you turn 65. If your birthday is on the first of the month, coverage can start the month before you turn 65. Coverage always starts on the first of a month.
Missed it? There's another window
If you miss your Initial Enrollment Period, you can usually sign up during the General Enrollment Period, January 1 to March 31 each year. That coverage starts the month after you sign up.
Want the detail? How it works, a worked example and common mix-ups are in .
Words on this page
Initial Enrollment Period
the 7-month window around your 65th birthday when you can first sign up for Medicare
General Enrollment Period
a yearly window, January 1 to March 31, to sign up if you missed your first chance
Who can answer for your situation
For a start date based on your exact birthday and situation, Social Security can walk you through it, or you can call 1-800-MEDICARE.
Shows why signing up on time matters, since late sign-up can add a lasting cost.
How the 7-month window works
The window is built around the month you turn 65. It covers the 3 months before that month, the month itself, and the 3 months after. That's 7 months in all.
During this time you can sign up for Part A (hospital insurance) and Part B (medical insurance).
If your birthday is on the first of the month, the window starts and ends a month earlier: 4 months before the month you turn 65 through 2 months after.
An example
Say your birthday is June 15. Your Initial Enrollment Period runs from March, 3 months before, through September, 3 months after. If you sign up in March, April, or May, your coverage can begin June 1.
If you miss your window
If you don't sign up when you're first eligible and don't qualify for another window, you can sign up during the General Enrollment Period, January 1 to March 31, and your coverage starts the month after you sign up.
Signing up late can also mean a lasting extra amount added to your premium, so it helps to know your window ahead of time.
Common mix-ups
These are the pairs people most often mix up.
Initial Enrollment vs. Open Enrollment
Your Initial Enrollment Period is a one-time window around your 65th birthday to first get Medicare. Open Enrollment, October 15 to December 7, is a yearly window to change plans, not to first sign up.
Still working at 65?
If you have health coverage from a job where you or your spouse still work, you may be able to wait to sign up without paying a late enrollment penalty, and use a Special Enrollment Period later instead.
Generally, you're first eligible to sign up for Part A and Part B starting 3 months before you turn 65 and ending 3 months after the month you turn 65.
Checked September 24, 2026
12 What the source says · When can I sign up for Medicare? (introduction)
Most people sign up for both Part A (Hospital Insurance) and Part B (Medical Insurance) when they're first eligible (usually when they turn 65).
2 What the source says · When does Medicare coverage start?
This is called your Initial Enrollment Period. It lasts for 7 months, starting 3 months before you turn 65, and ending 3 months after the month you turn 65.
Checked September 24, 2026
6 What the source says · When your coverage starts
The date your coverage starts depends on which month you sign up during your Initial Enrollment Period. Coverage always starts on the first of the month. If you qualify for premium-free Part A: Your Part A coverage starts the month you turn 65. (If your birthday is on the first of the month, coverage starts the month before you turn 65.)
Checked September 25, 2026
7 What the source says · Between January 1-March 31 each year (General Enrollment Period)
You can sign up between January 1-March 31 each year. This is called the General Enrollment Period. Your coverage starts the month after you sign up.
4 What the source says · If you (or your spouse) have health insurance from a job
If you or your spouse are still working, you may be able to wait to sign up for Medicare without paying a late enrollment penalty.
Checked September 24, 2026
8 What the source says · If you (or your spouse) have health insurance from a job
Once you stop working (or lose your health insurance, if that happens first) you have an 8-month Special Enrollment Period (SEP) when you can sign up for Medicare (or add Part B to existing Part A coverage).
9 What the source says · Section 1: How Medicare works, Initial Enrollment Period (p. 17)
If you sign up for Part A and/or Part B during the first 3 months of your Initial Enrollment Period, in most cases, your coverage begins the first day of your birthday month. However, if your birthday is on the first day of the month, your coverage starts the first day of the prior month.
Checked September 25, 2026
10 What the source says · Section 1: How Medicare works, Important! (p. 17)
Remember, in most cases, if you don't sign up for Part A (if you have to buy it) and Part B when you're first eligible, your enrollment may be delayed and you may have to pay a late enrollment penalty that's added to your monthly premium for as long as you have Part B
Checked September 25, 2026
11 What the source says · Section 1: How Medicare works, Initial Enrollment Period (p. 17)
If your birthday is on the first day of the month, your 7-month period starts 4 months before the month you turn 65, includes your birthday month, and ends 2 months after the month you turn 65.
Checked September 25, 2026
Something look wrong?
If something here doesn’t match what you’ve been told, please check with 1-800-MEDICARE, and let us know through our Contact page.
General education, not individualized advice. For your own situation, you can call 1-800-MEDICARE or your State Health Insurance Assistance Program (SHIP).
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