Medicare Enrollment Window Calculator
Enter your date of birth. Get your Initial Enrollment Period, the coverage start rule, your Medigap open enrollment window, and, if you are still working, the Special Enrollment Period that starts when your job or coverage ends.
Your dates
Three birthdays, three sets of windows
Computed with the same rules the tool uses. Notice the person born on the 1st.
| Born | Eligible | Initial Enrollment Period | Last day | Medigap window (if Part B starts on time) |
|---|---|---|---|---|
| November 14, 1961 | November 2026 | August 2026 – February 2027 | February 28, 2027 | November 2026 – April 2027 |
| June 1, 1961 | May 2026 (born on the 1st) | February 2026 – August 2026 | August 31, 2026 | May 2026 – October 2026 |
| March 20, 1962 | March 2027 | December 2026 – June 2027 | June 30, 2027 | March 2027 – August 2027 |
Still working: coverage ending March 31, 2027 gives a Special Enrollment Period through October 31, 2027; coverage ending December 15, 2026 gives one through July 31, 2027.
How the math works
Eligibility month = the month you turn 65 (the month before if born on the 1st). Initial Enrollment Period = eligibility month minus three through plus three. Coverage start: first of the eligibility month if you enroll before it; otherwise the first of the month after you enroll. Special Enrollment Period = the eight months starting the month after employment or the employer coverage ends, whichever is first. Medigap open enrollment = six months from the first month Part B is in effect at 65 or older. HSA: Part A enrollment after 65 is backdated up to six months (not before eligibility), and contributions for backdated months are excess.
Sources
This tool is educational and simplifies by design. It computes published Medicare rules for the inputs you enter; it does not know your full situation, is not insurance, tax, or legal advice, and does not recommend any action. Nothing you type is transmitted or stored — the math runs in your browser. Confirm your dates and amounts with Social Security (1-800-772-1213), Medicare (1-800-MEDICARE), or a licensed professional before acting.
Window questions, answered
When exactly does my Initial Enrollment Period run?
Seven months: the three months before the month you turn 65, your birthday month, and the three months after. Born on the 1st of a month? Medicare treats you as eligible the month before, and every window shifts back one month.
When does coverage start if I sign up early?
Sign up in the three months before your birthday month and Part B starts the first day of your birthday month. Sign up during your birthday month or the three months after and it starts the first of the month after you sign up (a rule change effective 2023).
I’m still working. When is my window?
As long as you have coverage from current employment (yours or your spouse’s, employer with 20+ employees) you can enroll any time. When that employment or coverage ends, an 8-month Special Enrollment Period begins; enroll in the first month or two so there is no gap.
What is the Medigap open enrollment window?
Six months, starting the month your Part B is effective at 65 or older. During it, any Medigap insurer must sell you any plan it offers at the standard rate regardless of health. Miss it and, in Utah, you can be underwritten or declined outside guaranteed-issue situations.
What if I miss everything?
The General Enrollment Period is January 1 to March 31 each year; coverage starts the first of the month after you sign up, and the Part B late penalty applies to the months you missed.
Related tools and guides
Still-working checker
Answer four questions to see whether you can delay Part B and what to ask HR.
Open the tool →Medicare and your HSA
The six-month lookback that surprises people who keep working.
Read the guide →
Talk it through before you decide
Bring your birth date, your work situation, and last year’s tax return. Leave knowing your enrollment window, what Medicare will cost you, and whether the income surcharge applies.
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