Birthday is not on the first
The seven-month window runs from three months before the birthday month through three months after it. If you enroll before the birthday month, coverage generally begins the first day of the birthday month.
Private, browser-based planning tool
Build Your Medicare Enrollment Timeline
Enter your birth date and current coverage situation to see an educational Initial Enrollment Period timeline, the questions that need verification, and the next official step.
Official rules and sources checked July 25, 2026Your answers stay in this browser and are not submitted.
Age-65 Medicare Enrollment Planner
Calculate your age-based Medicare eligibility month and seven-month Initial Enrollment Period. Then review the questions you should confirm before making a decision.
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Use this result for planning
This result is educational. It does not determine eligibility, your actual effective date, a penalty, or a Special Enrollment Period. Medicare can also be available before age 65 in situations this tool does not evaluate.
How the seven-month Initial Enrollment Period works
For most people who become eligible based on age, the Initial Enrollment Period begins three months before the month they turn 65, includes that month, and ends three months later.
Birthday is on the first
Medicare treats the prior month as the eligibility month. The window starts four months before the birthday month and ends two months after it; coverage may begin the first day of the prior month.
Enrollment later in the window
For Part B and premium Part A, enrolling during the eligibility month or the following three months generally starts coverage the next month. Confirm the date with Social Security.
Current employment coverage is the key distinction
A person covered by a group health plan based on their own or a spouse’s current employment may qualify for a Special Enrollment Period. COBRA, retiree coverage, and Marketplace coverage do not count as current-employment coverage for that Part B rule. Employer size and coordination rules can also affect the decision, so confirm with the employer benefits administrator and Social Security before delaying Part B.
Why HSA contributors need a separate check
Premium-free Part A can begin retroactively for up to six months when someone enrolls after 65, but not earlier than the first month of eligibility. Medicare enrollment can affect HSA contribution eligibility. Coordinate the stop date with Social Security, the employer, and a tax adviser before contributing.
After you know the dates, compare the coverage structure
Medicare enrollment timing and plan selection are separate decisions. Verify Part A and Part B dates first. Then compare provider access, prescriptions, travel needs, premiums, and out-of-pocket exposure.