While Original Medicare is the only insurance for some beneficiaries, it’s also common to have Original Medicare along with another type of insurance in order to reduce out-of-pocket costs, like Medicare Supplement or another federal program. When that happens, there’s a predetermined coordination of benefits, in which Original Medicare is the “primary insurance” and a supplemental plan is the “secondary insurance.” The primary insurance pays first, and the secondary insurance may then make additional payments before the policyholder owes money. That might include some portion of your deductibles or copayments, but it may not.

When is Original Medicare Primary Insurance?

If you don’t have any other insurance, Orignal Medicare will always be your primary insurance. In most cases, when you have multiple forms of insurance, Original Medicare will still be your primary insurance. Here are several common instances when Original Medicare will be the primary insurer.

If you have job-based insurance from a company with fewer than 20 employees.
Your group insurance plan is the secondary insurer, so you should enroll in Medicare Part B before your group plan will pay its portion of the claim.¹

If you have retiree insurance through a former company.
Some retiree insurance plans do not pay for medical costs if you’re eligible for Original Medicare and don’t enroll. To get the details of how Original Medicare will work with your retirement health benefits, get a copy of your plan’s benefit materials.²

If you have COBRA insurance after leaving a company where you had health insurance.
You may decide to keep only Original Medicare, and not pay for additional coverage through COBRA.

If you have a disability.
If you’re younger than 65, and your employer-based health plan has fewer than 100 employees, Medicare will pay first.³

If you have amyotrophic lateral sclerosis (ALS) or end-stage renal disease (ESRD).
Even if you have a group health plan, Original Medicare is the primary insurer as long as you’ve been eligible for Medicare for 24 months or more. ⁴

If you have TRICARE.
If you are on inactive duty, Original Medicare is the primary insurer, but TRICARE will pay the bills if you get services from a military hospital or other federal health care provider.⁵

If you have Medicaid.

Medicaid is always the secondary insurance if you have Medicare.⁶

When is Medicare Secondary Insurance
While Original Medicare usually is the primary insurance, there are some instances when a supplement to Medicare is secondary. Two common instances are:

If you have job-based insurance from an employer with 20 or more employees.

This is the case whether you get insurance through your company or your spouse’s employer. Employers must offer workers age 65 or older the same health benefits that they offer to the rest of employees.⁷

If you receive workers’ compensation.

Your workers’ compensation insurance will be primary for any services or items related to your workers’ compensation claim. Orignal Medicare will serve as your primary service for all covered medical expenses unrelated to that claim.⁸

You have Original Medicare and…	Primary Insurance	Secondary Insurance
…Medicaid	Original Medicare	Medicaid
… You are 65 or older and have a group health plan through an employer with 20 or more employees	Group health plan	Original Medicare
… You are 65 or older and have a group health plan through an employer with fewer than 20 employees	Original Medicare	Group health plan
… You and a retiree health plan through a former employer after you retire	Original Medicare	Retiree coverage
… You are disabled and have a group health plan through an employer with 100 or more employees	Group health plan	Original Medicare
… You are disabled and have a group health plan through an employer with fewer than 100 employees	Original Medicare	Group health plan
… You have veteran’s benefits	Original Medicare pays for Medicare-covered services Veteran’s Affairs pays for VA-authorized services	Typically does not apply
… You have COBRA coverage	Original Medicare	COBRA
… You have TRICARE and are active-duty military	TRICARE	Original Medicare
… You have TRICARE and are inactive duty military	Original Medicare	TRICARE may pay
… You have been in an accident and insurance is involved	No-fault or liability for services related to the accident claim	Medicare
…. You are covered by workers’ compensation	Workers’ compensation for services or items related to the workers’ compensation claim	Typically does not apply
… You have end-stage renal disease and a group health plan and have been eligible for Medicare for 30 months or less	Group health plan	Original Medicare
… You have end-stage renal disease and a group health plan and have been eligible for Medicare for more than 30 months	Original Medicare	Group health plan
… You have end-stage renal disease and COBRA coverage and have been eligible for Medicare for fewer than 30 months	COBRA	Original Medicare
… You have end-stage renal disease and COBRA and have been eligible for Medicare for more than 30 months	Original Medicare	COBRA
… You are covered under the Federal Black Lung Benefits Program	The Federal Black Lung Program pays for services related to Black Lung	Original Medicare

Source: “Your Guide to Who Pays First. .” Medicare.gov. Accessed September 13, 2023.

When can you delay enrolling in Original Medicare?

If you have health insurance through your or your spouse’s employer, and that employer has more than 20 employees, you may be able to delay enrolling in Original Medicare without paying a penalty. In that case, even if you did enroll in Original Medicare at age 65, it would be a secondary insurance and only kick in after your primary insurance paid its share of your claims. To avoid penalties after you (or your spouse) leave your job, you’ll need to enroll in Original Medicare within eight months. ⁹

If your employer has fewer than 20 employees, Original Medicare would be your primary insurance, and you should enroll during your Initial Enrollment Period. If you miss this chance to enroll in Medicare Part B, you may face a late enrollment penalty. Every year that you delay enrollment in Medicare Part B, your premiums will go up 10% unless you or your spouse have insurance through work.¹⁰

While having multiple forms of health insurance is a fortunate situation, it can also be confusing to determine which one is your primary and which is your secondary–or whether it makes sense to continue paying for both policies. Figuring out which insurance is your primary, however, will make it easier for you to manage your insurance going forward.