Medicare and Employer Coverage

Medicare and employer coverage can work together after you turn 65, but which one pays first depends almost entirely on how many people your employer has on payroll. If your employer has 20 or more employees, your group health plan usually stays primary, which means you can often delay Medicare Part B without triggering the late enrollment penalty. If your employer has fewer than 20 employees, Medicare typically becomes primary once you turn 65, and delaying Part B can leave real gaps in what gets paid. Working into your late 60s and beyond is common, and knowing which side of that 20-employee line you fall on is the first decision to make.

Medicare uses a specific rule to decide which plan pays a claim first when you have both Medicare and employer coverage: employer size. According to Medicare.gov, if your employer has 20 or more employees, the employer group health plan pays first and Medicare pays second for active employees age 65 and older. If your employer has fewer than 20 employees, Medicare pays first and the employer plan pays second, regardless of whether you have already enrolled.

This matters because a plan that pays second will often deny or reduce a claim if you were supposed to have Medicare in place as your primary coverage. That is how people end up with unexpected bills after skipping Part B when they should not have.

If your employer has 20 or more employees: your employer coverage is primary and Medicare is secondary. Many people in this situation delay Part B to avoid the monthly premium and keep their employer plan as their only coverage. You can do this without a Part B late penalty as long as you sign up within 8 months after your employment or employer coverage ends, which is your Special Enrollment Period. If your employer's drug coverage is creditable, meaning it is considered at least as good as Medicare's standard Part D benefit, you can also delay Part D enrollment. See our late enrollment penalty guide for how the timeline works if you wait too long.

If your employer has fewer than 20 employees: Medicare becomes primary at 65, so you generally should enroll in Part A and Part B during your Initial Enrollment Period, the seven-month window centered on your 65th birthday. Your employer coverage then pays second. If you delay Part B in this situation, you can end up with coverage gaps that your employer plan does not fully cover, because it is designed to supplement Medicare rather than replace it.

Creditable prescription drug coverage is employer or union drug coverage that is considered at least as good as Medicare's standard Part D benefit, which lets you delay Part D enrollment without a late penalty. Your employer or plan administrator is required to send you a notice each year stating whether your drug coverage is creditable. Keep that notice, since you may need to show it later if you enroll in Part D and are asked whether you had continuous creditable coverage.

Dropping employer coverage to rely on Medicare can also affect a spouse who is covered under your plan. If your spouse is not yet 65 and not otherwise eligible for Medicare, losing the employer plan may mean they need to find coverage through the ACA marketplace or their own employer. Confirm this with your benefits administrator before you make a final decision. If your spouse later needs to enroll in Medicare on their own, our guide on enrolling in Medicare after losing employer coverage walks through that Special Enrollment Period.