Does employer size affect whether I need to take Part B at 65?
The short answer
Yes, employer size matters a lot. If you work for a company with 20 or more employees, your group health plan is primary and you can usually delay Part B without penalty. With fewer than 20 employees, Medicare pays first and delaying Part B can create serious coverage gaps.
The full explanation
This is one of the most important and most misunderstood rules in Medicare. When you turn 65 and still have coverage through an employer, what you should do about Part B depends on how many people your employer has on payroll. If the company has 20 or more employees, the group health plan is considered the primary payer, meaning it pays your claims first. In that case, you can delay enrolling in Part B without any penalty, as long as you sign up within eight months of losing that coverage or leaving the job. But if the employer has fewer than 20 employees, Medicare becomes the primary payer by law. That means your group plan may pay little or nothing on claims until Medicare has paid its share. If you haven't enrolled in Part B, you could end up stuck with large unpaid bills. The employer size rule also applies to people on a spouse's employer plan, so the spouse's employer headcount is what matters, not the size of the company you worked for. When in doubt, ask your HR department or benefits administrator in writing whether Medicare is primary or secondary for your specific plan.
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