Your Medicare sign-up window at 65

Enter your birth date. You will see the seven months of your Initial Enrollment Period, and for each month, the day your Part B coverage would start if you signed up then.

How the window is worked out

Your Initial Enrollment Period is seven months long. It starts three months before the month you turn 65, includes that month, and ends three months after it.¹

The tool applies one rule that trips people up. Social Security counts you as reaching an age on the day before your birthday.² If you were born on the 1st of a month, you count as turning 65 in the month before, so your window starts four months before your birthday month and ends two months after.³ Born on January 1? Your Medicare month is December of the year before.

Why each month shows a different start date

For everyone who turned 65 in January 2023 or later, the rule is simple. Sign up in any of the first three months and Part B starts on the first day of the month you turn 65. Sign up in that month or any of the three after it, and Part B starts on the first day of the next month.⁴

So the only way to have no gap between turning 65 and coverage starting is to sign up in the first three months. Each month you wait after that pushes the start back a month.

If you turned 65 before January 2023, an older rule set your dates, and the tool shows the dates it gave. Under it, signing up in the last three months of the window started Part B two or three months after the month you signed up.⁴

Premium-free Part A follows its own rule: it starts the month you turn 65, and if you sign up for it later it can reach back up to six months, but not to before 65.⁵

What the tool doesn't know

Whether you have job-based coverage. If you or your spouse are still working and covered by that employer's plan, you may be able to sign up for Part B later without a penalty.⁶ See Still working at 65.
Whether you will be signed up automatically. If you get Social Security benefits at least four months before you turn 65, Parts A and B start automatically.⁷
Medicare before 65. People who qualify through a disability, End-Stage Renal Disease or ALS follow different timing.⁸ This tool covers the window at 65 only.

If the window has passed

If your seven months are behind you and you didn't sign up or qualify for a Special Enrollment Period, the next chance is the General Enrollment Period, January 1 to March 31. Coverage starts the month after you sign up, and a late penalty may apply.⁹ The penalty estimate shows what it might be.

Your birth date stays on this computer

The calculation runs in your browser. The date you enter isn't sent anywhere, isn't stored, and isn't added to the page address. Close the page and it is gone.

Other tools

Part B late-enrollment penalty estimateEstimate the Part B late-enrollment penalty: the months that count, the full 12-month periods, the percentage, and what it adds to the current standard premium.
Full retirement age: your month, and what starting early or late doesEnter your birth date to find your Social Security full retirement age, the month you reach it, the earliest month you can start, and the percentage of your full benefit at every age from 62 to 70.
RMD age by birth year: when required minimum distributions startEnter your birth date to find the age your required minimum distributions start, the year of your first RMD, and its deadline. With the full table by birth date.
All your dates on one pageThe planner: every date from 50 to 75, worked out from your birthday, ready to print.

Sources for this page

Initial Enrollment Period: seven months around the month you turn 65. Source: Electronic Code of Federal Regulations, 42 CFR 407.14: Initial enrollment period; Medicare.gov, When does Medicare coverage start?. Checked October 25, 2026.
Social Security counts you as reaching an age the day before your birthday. Source: Electronic Code of Federal Regulations, 20 CFR 404.2(c)(4): Attainment of age. Checked October 25, 2026.
Birthday on the 1st: the window starts and ends a month earlier. Source: Medicare.gov, When does Medicare coverage start?; Electronic Code of Federal Regulations, 20 CFR 404.2(c)(4): Attainment of age. Checked October 25, 2026.
When Part B starts, by the month you sign up: for people who turned 65 from January 2023, the first 3 months of the window give the month you turn 65 and the last 4 the month after you sign up; before January 2023, the last 3 months gave 2 or 3 months after you sign up. Source: Electronic Code of Federal Regulations, 42 CFR 407.25: Beginning of entitlement; Medicare.gov, When does Medicare coverage start?. Checked October 25, 2026.
Premium-free Part A starts the month you turn 65; signing up later, it reaches back up to 6 months (not before 65). Source: Medicare.gov, When does Medicare coverage start?. Checked October 25, 2026.
Special Enrollment Period for job-based coverage: any time while covered, or 8 months after the job or the coverage ends, whichever is first. Source: Medicare.gov, When does Medicare coverage start?; Medicare.gov, When can I sign up for Medicare?. Checked October 25, 2026.
Getting Social Security at least 4 months before 65 signs you up for Parts A and B automatically. Source: Medicare.gov, How do I sign up for Medicare?. Checked October 25, 2026.
Medicare before 65 through a disability, End-Stage Renal Disease or ALS has its own timing. Source: Medicare.gov, Joining a plan; Medicare.gov, How do I sign up for Medicare?. Checked October 25, 2026.
General Enrollment Period: January 1 to March 31; coverage starts the month after you sign up. Source: Electronic Code of Federal Regulations, 42 CFR 407.15: General enrollment period; Medicare.gov, When does Medicare coverage start?. Checked October 25, 2026.

Every figure on the site, with its source and checked date, is on the sources page.