When do I sign up for Medicare, and what happens if I'm late?

The Initial Enrollment Period lasts 7 months: it starts 3 months before the month you turn 65 and ends 3 months after it. If you sign up before your birthday month, Part B starts the month you turn 65. If you already get Social Security, enrollment is automatic.

Miss it and you wait for the General Enrollment Period, January 1 to March 31, with coverage starting the month after you sign up. The Part B penalty is 10% of the standard premium for each full 12-month period you could have had Part B and did not, and it lasts as long as you have Part B. Two full years late means 20% more. On the 2026 premium of $202.90, that is about $40.58 extra a month.

Part D has its own penalty. Go 63 days or more in a row without Part D or other creditable drug coverage after your initial period, and you owe 1% of the national base beneficiary premium ($38.99 in 2026) for each full month without coverage. Medicare's example: 17 months uncovered adds $6.60 a month, permanently.

The main exception is current job coverage. If you or your spouse are still working and covered by that employer's plan, and the employer has 20 or more employees, you can delay Part B without penalty and sign up within 8 months after the job or the coverage ends. With an employer of fewer than 20 employees, Medicare warns that the job plan might not pay for health services unless you have both Part A and Part B.

The trap: COBRA and retiree coverage do not count as current employment coverage. Your 8-month window starts when you stop working, even if you keep COBRA.