Whether you need to sign up for Medicare at 65 while still working depends on your employer’s size and insurance coverage. If you or your spouse work for a company with 20 or more employees and have health insurance through that job, you can delay Medicare Part B enrollment without penalty until you stop working or lose that coverage. However, if you work for a company with fewer than 20 employees, you must enroll in Medicare Part B during your Initial Enrollment Period or face a 10% penalty for each full 12-month period you delay. This is because Medicare becomes the primary payer for smaller employer groups. If you have health insurance that’s not employer-based, such as Medicaid or Marketplace coverage, the rules vary by insurance type. It’s crucial to contact Medicare or a licensed agent to understand your specific situation, as making the wrong decision about enrollment timing can result in permanent monthly penalties and gaps in coverage.