Short answer: It depends on your employer’s size. If your employer has 20 or more employees and you have active group coverage, you can usually delay Medicare without penalty. If the employer has fewer than 20 employees, Medicare generally pays first, so you should enroll at 65 to avoid gaps and penalties.
The deciding factor is whether your group plan or Medicare pays first. At an employer with 20 or more employees, the group plan is primary, so you can keep it and delay Medicare Part B without a late penalty, signing up later through a Special Enrollment Period when you retire.
At an employer with fewer than 20 employees, Medicare is usually primary, meaning if you don’t enroll at 65, you could be left with little effective coverage. Many people take premium-free Part A at 65 regardless, but be careful: enrolling in any part of Medicare ends your ability to contribute to an HSA. Coordinate the decision with your employer’s benefits team.
Sources
- CMS, Medicare Secondary Payer rules (42 U.S.C. §1395y(b)); Medicare knowledge base.
Content history
Originally published: June 16, 2026
Last reviewed: June 16, 2026