MEDICARE
Your Medicare timeline, month by month
Enrollment windows, the birthday-on-the-first rule, the Part B premium, and what changes each fall.
By Charles Mungovan, Founder, licensed insurance producer · Published 2026-08-14 · Last reviewed 2026-08-14
The Initial Enrollment Period
The Initial Enrollment Period generally begins three months before the month a person turns 65, includes the birthday month, and continues for three months after — seven months in total. Enrolling in the first three months generally means coverage starts the month of the 65th birthday.
There is an exception worth knowing: if a birthday falls on the first day of a month, Medicare treats the person as turning 65 in the previous month, so the enrollment window and the coverage start date shift one month earlier.
Parts A and B
Part A covers inpatient hospital care and is premium-free for people who have enough work history through Medicare-covered employment; others may pay a premium. Part B covers outpatient and physician services and has a monthly premium that can be higher for higher-income beneficiaries. Together, Parts A and B are Original Medicare.
Anyone still working at 65 with employer coverage should confirm in writing whether Part B can be delayed without a late-enrollment penalty. The answer depends on the employer and the plan.
Then a decision
Medicare Advantage is a private-plan alternative for receiving Medicare Part A and Part B benefits. A person remains enrolled in Medicare and must generally continue paying the Part B premium. The alternative is keeping Original Medicare and adding a Medigap policy, usually with a separate Part D prescription plan.
- Medicare Advantage: plan-specific networks, referral rules, and prior-authorization requirements; often includes prescription coverage; benefits and costs can change annually.
- Medigap plus Part D: Medigap covers certain Original Medicare cost sharing; providers who accept Medicare generally accept Medigap; premiums are typically higher and a separate drug plan is needed.
Each fall
The Annual Enrollment Period runs October 15 through December 7, with changes generally effective January 1. Plan documents for the coming year are the authoritative source for costs, networks, and drug lists.
Neutral help
Medicare.gov and 1-800-MEDICARE provide official information, and every state has a State Health Insurance Assistance Program (SHIP) that offers free counseling.
Educational information only. This page is not individualized insurance, investment, tax, legal, or accounting advice, and it is not a recommendation to buy or replace any product.