People working past the age of 65 and those under 65 who are working and receiving disability are eligible to receive Medicare insurance, according to the National Council on Aging. There are several rules regarding which insurance pays first if Medicare recipients are also covered by additional insurance, such as an employee health plan, according to Medicare.gov.
If Medicare recipients also receive health coverage from their employer or their spouses' employer, and those companies employee 20 or more people, the group plans pay first with Medicare covering the remaining expenses up to the Medicare-approved amount, according to Medicare.gov. These companies must offer the same benefits to employees age 65 and older as what they offer their younger workers. Medicare usually pays first if recipients work for companies with fewer than 20 employees, but there are exceptions if companies have joined together to purchase coverage in a group that consists of 100 or more employees.
Medicare also pays first for recipients who are retired and have health plans under former employers, and it covers recipients who have declined coverage in group plans offered by their employers, according to Medicare.gov. For people under the age of 65 who receive Medicare due to disabilities, Medicare covers medical expenses first if group coverage is through companies with fewer than 100 employees. If recipients who are disabled and under age 65 receive large group insurance, Medicare pays after the group plan.