When Can You Enroll in Medicare?

Your Initial Enrollment Period is seven months long: the three months before the month you turn 65, your birthday month, and the three months after. If your birthday is on the 1st of the month, Medicare treats you as turning 65 the month before, and the whole window shifts a month earlier. The calculator above works this out from your date of birth.

Since January 2023 the rule is simple. Your eligibility month is the month you turn 65 — or the month before, if your birthday is on the 1st. Enroll during the three months before your eligibility month and coverage begins on the 1st of that eligibility month. Enroll during the eligibility month or the three months after and coverage begins on the 1st of the month after you sign up. That's why enrolling early in the window avoids any gap.

No. If you or your spouse are covered by a plan from a current employer — a job one of you still works at — you can delay Part B without a penalty, whatever the employer's size, and you get an 8-month Special Enrollment Period when the job or the coverage ends. Employer size decides who pays first: with 20 or more employees the plan pays before Medicare, so delaying saves the Part B premium; with fewer than 20, Medicare pays first, so most people enroll at 65 anyway. Most people take Part A at 65 because it's premium-free, unless they're contributing to a Health Savings Account, which Medicare enrollment stops. COBRA and retiree coverage do not count as current employment, so they don't let you delay without penalty.

Without a Special Enrollment Period, you wait for the General Enrollment Period, January 1 through March 31 each year, and coverage starts the month after you enroll. You'll also owe a Part B late-enrollment penalty: 10% of the standard Part B premium for each full 12-month period you could have had Part B but didn't, added to your premium for as long as you have Part B.

Not if your benefits began before you turn 65: Medicare then enrolls you in Parts A and B automatically and mails your card about three months before your eligibility month. If you start Social Security at 65 or later, you apply for Medicare yourself. The packet explains how to decline Part B if you have employer coverage and want to delay it.

Your Medigap open enrollment period lasts six months and starts the first month you're 65 or older and enrolled in Part B. During that window an insurer must sell you any Medigap policy it offers at the best available rate, with no health questions. After it ends, most states let insurers ask health questions or decline you, so it's the one window that doesn't come around again.

The Annual Enrollment Period runs October 15 through December 7 every year. It's when anyone on Medicare can join, switch or drop a Medicare Advantage or Part D drug plan, with changes effective January 1. Medicare Advantage Open Enrollment, January 1 through March 31, lets people already on an Advantage plan make one switch or return to Original Medicare.