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Medicare enrolment window finder
Your birth month sets a seven-month window. A job, a COBRA plan or a coverage end date can replace it with a different one entirely. Enter both and see which clock you are actually on.
- Exact months, not rules of thumb
- Handles employer cover
- Flags the COBRA trap
Find your window
When does yours open, and when does it shut?
Your enrolment window
March 2027 to September 2027
Seven months: the three before the month you turn 65, that month, and the three after. Sign up in the first three and cover starts 1 June 2027.
- Month you turn 65
- June 2027
- Initial Enrolment Period — 7 months
- March 2027 to September 2027
- Sign up in the first 3 months
- Cover starts 1 June 2027
- Sign up in the last 4 months
- Cover starts the first of the month after you sign up
- If you miss the whole window
- General Enrolment Period, 1 January to 31 March, with a lifelong Part B penalty
Your 6-month Medigap open enrolment starts the day Part B starts — that is the only time a supplement cannot ask health questions.
The windows
Six clocks, and only some of them repeat
People talk about "the Medicare deadline" as though there were one. There are six, they have different lengths, and two of them happen once in your life and never again.
Initial Enrolment Period = the 3 months before the month you turn 65, that month, and the 3 after
The two that never repeat are the Initial Enrolment Period and the six-month Medigap open enrolment that starts the day Part B does. Miss the second and a supplement can ask health questions for the rest of your life — which is the part nobody warns you about.
| Window | How long | What it is | Cover starts |
|---|---|---|---|
| Initial Enrolment Period | 7 months around your 65th birthday | The three months before the month you turn 65, that month, and the three after. | Sign up in the first three months and cover starts the first of your birthday month. |
| Special Enrolment Period — still working | 8 months for Part B | From the month after the job or the group plan ends, whichever comes first. Needs an employer of 20 or more. | Usually the first of the month after you enrol, or you can ask for it to be backdated. |
| Special Enrolment Period — Part D | 63 days | From the end of creditable drug coverage. Far shorter than the Part B window and easy to miss. | The first of the month after you join a plan. |
| General Enrolment Period | 1 January to 31 March | The fallback if you miss everything else. A lifelong Part B penalty usually follows. | The first of the month after you sign up. |
| Medigap open enrolment | 6 months | From the day Part B starts. The only window where a supplement cannot ask health questions. | Not repeatable — it happens once. |
| Annual Enrolment Period | 15 October to 7 December | For changing Advantage and Part D plans once you are already enrolled. Not a way to join Medicare late. | 1 January. |
The traps
What people ask about timing
Medicare treats you as turning 65 in the previous month when your birthday falls on the first. That moves the whole seven-month window a month earlier — tick the box and the dates above adjust.
No, and this is the most expensive misunderstanding in Medicare. Only active coverage from current employment — yours or your spouse's, at an employer with 20 or more staff — protects you. COBRA and retiree plans do not, so the penalty clock runs the whole time.
Yes. At a small employer Medicare usually pays first, so you normally need Part A and Part B at 65 even though you are still working. Confirm it with the plan administrator in writing before you decline anything.
Form CMS-L564, completed by the employer, plus form CMS-40B for you. Ask for the L564 before you leave the job — it is far harder to get afterwards.
2026 plan year
The figures this calculator uses
Sample figures for the 2026 plan year. Medicare and the Marketplace reset these every autumn.
- Initial Enrolment Period
- 7 months — 3 before, the birth month, 3 after
- Special Enrolment Period, Part B
- 8 months after employment or group cover ends
- Special Enrolment Period, Part D
- 63 days after creditable drug cover ends
- General Enrolment Period
- 1 January to 31 March, every year
Every figure above is a sample for the 2026 plan year on a demonstration site. Medicare publishes the real ones each autumn at Medicare.gov, and they change every year.