When do I have to enroll in Medicare and what happens if I miss the deadline?

Your Initial Enrollment Period is a seven-month window around your 65th birthday. If you're not covered by active employer insurance, missing it can trigger lifelong late-enrollment penalties: Part B adds 10% to your premium for each 12-month period you delayed, and it never goes away. Part D has its own penalty. If you keep working past 65 with qualifying employer coverage, you can delay penalty-free and enroll later through a Special Enrollment Period, but retiree coverage and COBRA do not count as active employer coverage for this purpose. Missing the deadline is a common and expensive mistake, so confirm your timing with medicare.gov or the Social Security Administration well before you turn 65.