When Can I Enroll in Medicare Part B?

Most people first become eligible for Medicare Part B around their 65th birthday. Your Initial Enrollment Period lasts seven months: it opens three months before the month you turn 65, includes your birthday month, and closes three months after. If you sign up during the three months before your birthday month, coverage starts the first day of the month you turn 65.

Part B always carries a monthly premium, which is $202.90 for most people in 2026, along with a $283 annual deductible. CMS announces the final 2027 figures in late September 2026. Part A, by contrast, is premium free for most people who have worked and paid Medicare taxes for at least 40 quarters. If you are already receiving Social Security benefits when you turn 65, you are typically enrolled in Parts A and B automatically.

If you or your spouse are still actively working and you have health coverage through that employer, you can usually delay Part B without penalty. When the job or the coverage ends, whichever comes first, you get an eight month Special Enrollment Period to sign up for Part B with no late penalty.

Here is the caveat that catches people: COBRA and retiree coverage do not count as active employer coverage. If you keep COBRA after leaving a job and wait to enroll in Part B, you can end up with both a gap in coverage and a late penalty. Coverage through a small employer can also work differently, because Medicare may be expected to pay first, so confirm how your plan coordinates with Medicare before you decide to delay.

If you miss both your Initial Enrollment Period and any Special Enrollment Period, you can still sign up during the General Enrollment Period, which runs January 1 to March 31 each year, with coverage starting the month after you enroll. The bigger issue is the late enrollment penalty: it is added to your Part B premium, it grows the longer you went without coverage, and it lasts for as long as you have Part B.

Because the stakes are permanent, it pays to map out your dates before you get close to 65. A licensed advisor can look at your work situation and tell you exactly when your windows open and close, at no cost to you.