If you're eligible for Medicare when you turn 65, you can sign up during the 7-month period that begins 3 months before the month you turn 65, includes the month you turn 65, and ends 3 months after the month you turn 65.
You can sign up for free Part A (if you’re eligible) any time during or after your Initial Enrollment Period starts. Your coverage start date will depend on when you sign up. If you have to buy Part A and/or Part B, you can only sign up during a valid enrollment period.
In most cases, if you don’t sign up for Medicare Part B when you’re first eligible, you’ll have to pay a late enrollment penalty for as long as you have Part B and could have a gap in your health coverage.
To sign up for Part B, complete an Application for Enrollment in Part B (CMS-40B). If you don't have Medicare or you want to sign up for Part A (some people have to pay a premium for Part A), contact Social Security.
Once your Initial Enrollment Period ends, you may have the chance to sign up for Medicare during a Special Enrollment Period. If you're covered under a group health plan based on current employment, you have a Special Enrollment Period to sign up for Part A and/or Part B any time as long as you or your spouse (or family member if you're disabled) is working, and you're covered by a group health plan through the employer or union based on that work.
You also have an 8-month Special Enrollment Period to sign up for Part A and/or Part B that starts the month after the employment ends or the group health plan insurance based on current employment ends, whichever happens first. Usually, you don't pay a late enrollment penalty if you sign up during a Special Enrollment Period.
COBRA and retiree health plans aren't considered coverage based on current employment. You're not eligible for a Special Enrollment Period when that coverage ends. This Special Enrollment Period also doesn't apply to people with End-Stage Renal Disease (ESRD)