Understand your timeline, avoid penalties, and enroll with confidence.
Figuring out when to enroll in Medicare is one of the most important decisions you'll make around age 65. The wrong timing can mean lifetime penalties; the right timing keeps your premiums low and your coverage uninterrupted.
Most people start with their Initial Enrollment Period, a 7-month window that opens three months before the month you turn 65. If you're turning 65 Medicare eligible and still working with strong employer coverage, you may be able to delay Part B without penalty — but the rules for small-employer plans and COBRA are different and often misunderstood.
The other Medicare enrollment periods matter too. The Annual Enrollment Period (October 15 – December 7) is when anyone already on Medicare can change Medicare Advantage or Part D plans for the coming year. The Open Enrollment Period (January 1 – March 31) gives Medicare Advantage members one shot to switch plans or return to Original Medicare. Special Enrollment Periods cover life events like moving, losing employer coverage, or becoming eligible for Extra Help.
Missing Medicare deadlines isn't just a paperwork problem. It creates coverage gaps, permanent premium surcharges, and months without drug or medical coverage. Use the Part B Penalty Calculator further down this page to see exactly what a delay would cost you.
Medicare is rules-based. Each enrollment period has its own window, purpose, and action list. Here are the four that matter most.
Enter your birth month and year to see exactly when your Initial Enrollment Period opens, closes, and when Part B starts.
Missed deadlines have real consequences. Here's what's at stake.
Go 63 or more consecutive days without creditable drug coverage and Medicare adds 1% of the national base premium for every month you went uncovered. The surcharge sticks for as long as you have Part D.
Missing your window can leave you without medical or drug coverage until the next General Enrollment Period (January 1 – March 31) — and Part B coverage wouldn't start until July 1 of that year.
Part B adds 10% to your premium for every full 12-month period you could have had it without creditable coverage. The surcharge is permanent for as long as you have Part B — meaning a multi-year delay can cost thousands across your Medicare years.
Medicare timing depends on your situation. Open the one that sounds like yours.
If your employer plan covers 20 or more employees, Medicare is usually secondary and you can generally delay Part B without a penalty. You'll have a Special Enrollment Period when the employer coverage ends.
If your employer has under 20 employees, Medicare is usually primary — enrolling on time is important to avoid coverage gaps and penalties.
When you leave employer coverage, you get an 8-month Special Enrollment Period for Part B. But drug coverage has its own 63-day rule — go longer than that without creditable Part D and the permanent Part D penalty starts accruing.
Plan your Medicare start date to line up with your last day of employer coverage so there's no gap.
If you're already collecting Social Security when you turn 65, Medicare Parts A and B are generally auto-enrolled for you — you don't need to sign up manually.
You'll still need to actively choose a Part D plan or a Medicare Advantage plan with drug coverage during your IEP to avoid the Part D late-enrollment penalty.
You're not out of options. Depending on the reason, you may qualify for a Special Enrollment Period or request equitable relief from Social Security to roll back a penalty.
General Enrollment runs January 1 – March 31 each year for Part B, with coverage starting the month after you enroll.
Quick answers to the enrollment questions we hear most.
