Medicare Initial Enrollment Period (IEP) Calculator
Your Initial Enrollment Period (IEP) is the seven months around your 65th birthday. It runs from three months before your birthday month through three months after it. Sign up in the first three months and Part B starts the first of your birthday month. Sign up later and it starts the first of the month after you enroll.
This page turns your birthday into the seven-month Initial Enrollment Period for Medicare Part A and Part B. Choose a birth month and birth year, press Calculate, and it lays out all seven months in order — the three before your birthday month, the birthday month itself, and the three after — then names the first and last month of the window.
It adds two rules you can act on. Enrolling in the first three months starts coverage on the first of your birthday month; enrolling in your birthday month or later pushes coverage to the first of the month after you sign up. And missing the window without a qualifying exception adds ten percent to your Part B premium for each full twelve-month period you were eligible and not enrolled, permanently.
All it needs is the month and year you were born. One optional switch, for people with — or recently off — active employer coverage, adds the Special Enrollment Period rules: the 20-employee rule for delaying Part B, the eight-month window that opens the month after the job or that coverage ends, whichever comes first, the shorter two-month window for Advantage and drug plans, and the warning that COBRA and retiree coverage do not count.
A checkbox for people born on the first applies Medicare's rule that moves the whole window a month earlier. It is an estimate; an optional form invites a callback. It quotes no premium, compares no plans, and cannot enroll anyone — Social Security sets your real dates.
Frequently asked questions
When does my Initial Enrollment Period start and end?
It opens three months before the month you turn 65. It closes at the end of the third month after that month — seven months in all. If you were born on the first of a month, Medicare treats you as turning 65 the month before. The whole window then shifts a month earlier.
What happens if I miss my Initial Enrollment Period?
Without a Special Enrollment Period, you wait for the General Enrollment Period. It runs January 1 through March 31. Part B may then carry a late-enrollment penalty: 10% of the standard premium for each full 12-month period you delayed.
Can I delay Part B if I am still working at 65?
You can usually delay Part B with coverage from your or a spouse's current employer of 20 or more employees. At a smaller one, Medicare usually pays first, so enroll on time. When the job or coverage ends, Part B allows 8 months; Advantage and drug plans allow 2. COBRA and retiree plans don't count.
Do I have to sign up for Part A at 65?
Most people take premium-free Part A at 65. One exception matters: contributions to a health savings account must stop once Part A begins, and Part A can start up to six months retroactively.
Updated September 27, 2026.