Coordination of benefits (COB) is the set of rules that decides which health plan is primary and which is secondary when the same person is covered by two plans. The primary plan processes the claim first under its normal terms. The secondary plan then looks at what is left and may pay some or all of it, up to its own limits. Couples with two employer plans, families with a child on both parents' plans, and people holding a Marketplace plan beside a spouse's job coverage all run into these rules in 2026 and 2027.
Adults under 65 and their children are the focus of this guide, which explains the order rules from the National Association of Insurance Commissioners (NAIC) model regulation that most states and insurers follow, the birthday rule for children, and how a Marketplace plan changes the picture. If you or a family member has Medicare, read the separate guide on Medicare coordination of benefits and who pays first. For subsidy questions, see can I get an ACA subsidy with an employer offer.
Coverage Breakdown
Direct answer: which health insurance pays first (2026-2027)
It depends on how each plan covers you. Your own employer plan pays first, and a spouse's plan covering you as a dependent pays second. For a child, the birthday rule applies: the plan of the parent whose birthday falls earlier in the calendar year is primary, unless a court order says otherwise. Active job coverage pays before COBRA. Confirm the order with both insurers.
How coordination of benefits works when you have two plans
Coordination of benefits applies the moment two group or individual plans cover the same person for the same service. The primary plan pays as if the other plan did not exist. The secondary plan then reviews the bill and the primary plan's payment, and may cover part of the remaining deductible, copay, or coinsurance. Together the two plans generally cannot pay more than the total allowable charge for the service, so having two plans does not mean the second one pays the same amount again.
Two plans from ACA-compliant insurers cannot refuse you over a preexisting condition, and both must include the essential health benefits when they are individual or small-group plans. What changes with two plans is who processes the claim first. Tell every doctor, hospital, and pharmacy about both plans and show both cards, because the provider bills the primary plan first. When plans disagree about the order, claims are often denied or delayed until you give each insurer the other plan's details. Insurers commonly mail a coordination questionnaire once a second plan appears, and answering it promptly keeps claims moving.
Who pays first: the order rules for adults (2026-2027)
The NAIC model regulation, which most states have adopted in some form for 2026 and 2027, sets the order for adults in a fixed sequence. The first rule that settles the question controls, and the later rules are only used when the earlier ones do not decide. Because self-funded employer plans follow federal rather than state insurance law, a plan's own document can differ in small ways, so the summary plan description is the final word for your plan.
- Own coverage before dependent coverage: the plan that covers you as the employee, member, or policyholder pays before a plan that covers you as a spouse or dependent.
- Active employee before COBRA: coverage through a current job pays before COBRA or state continuation coverage, which is secondary.
- Active before retiree or laid-off coverage: a plan for a working employee generally pays before a plan covering the same person as a retiree or laid-off worker.
- Longer coverage first: if none of the rules above settles it, the plan that has covered you for the longer period is primary, and successive plans count as one if the gap is under 24 hours.
- Equal sharing: if every rule fails to decide, the plans share the allowable expenses equally.
The birthday rule for children and divorced parents (2026-2027)
When a child is covered by both parents' plans and the parents are married or living together, the birthday rule makes the plan of the parent whose birthday falls earlier in the calendar year the primary plan. Only the month and day count, not the year of birth: a parent born on March 3 in 1990 is ahead of a parent born on June 20 in 1982. If both parents share the same birthday, the plan that has covered a parent longer is primary. The rule is by calendar position, not by which parent earns more or which plan is better.
Divorced or separated parents follow a different order. If a court decree makes one parent responsible for the child's health care and that parent's plan knows about the decree, that plan is primary, and so is that parent's spouse's plan if the parent has no coverage for the child. If the decree makes both parents responsible, or gives joint custody without naming one, the birthday rule decides. With no decree, the order is the custodial parent's plan, the custodial parent's spouse's plan, the non-custodial parent's plan, and then the non-custodial parent's spouse's plan. Send each insurer a copy of the decree, because a plan is not bound by terms it has not been told about during a plan year.
Marketplace plan plus an employer or spouse plan (2026 and 2027 coverage)
A Marketplace plan beside job-based coverage raises a subsidy question before a claims question. For a Marketplace plan under the ACA, if you enroll in an employer plan that counts as minimum essential coverage, you are not eligible for the premium tax credit for your own Marketplace coverage, even if the employer plan is unaffordable, according to the IRS Premium Tax Credit questions and answers. An offer of affordable job coverage that meets minimum standards also blocks the credit for you whether or not you enroll. Employer coverage counts as affordable when the employee's cost is under 9.96% of household income for 2026 coverage and 10.22% for 2027 coverage.
Family members are tested separately. The IRS says a relative who is not enrolled in the employer plan may still qualify for a credit on Marketplace coverage, but family members who could have joined affordable coverage through the employee's plan generally cannot. For them, affordability uses the employee's cost for family coverage. Sold from November 1, 2026, 2027 Marketplace plans use the 2026 poverty guidelines, while 2026 plans use the 2025 guidelines. Which plan pays first when you keep both depends on the contracts: individual Marketplace policies write their own coordination terms, so ask both insurers for the order in writing and confirm it before a large claim.
When Original Medicare or Medicaid is one of the two plans
Adults under 65 usually reach Medicare through disability or end-stage renal disease, and the order then depends on employer size. For Medicare based on disability, Medicare.gov says a large group health plan from current employment with 100 or more employees pays first and Original Medicare (Medicare Part A and Medicare Part B) pays second; below 100 employees, Medicare pays first. For people 65 and older, the cutoff is 20 employees. Medicare Advantage, Part D drug plans, and Medigap follow their own coordination terms, and Medigap generally pays after Original Medicare. The separate guide on Medicare coordination of benefits covers these cases in detail.
Medicaid and CHIP are generally the payer of last resort. According to Medicaid.gov, a state Medicaid program pays for covered services only after other liable coverage, such as an employer plan, has paid. A child with an employer plan and Medicaid or CHIP therefore bills the employer plan first. Tell the Medicaid agency about any other insurance, because it assigns third-party payment rights to the state and uses the information to avoid paying claims another plan owes.
Alternatives if two plans cost too much or overlap
Keeping two plans is a choice, not a requirement, and many households find the second premium does not buy enough extra protection in 2026 or 2027. Compare the premiums, deductibles, out-of-pocket maximums, and provider networks of each plan before paying twice. Five alternatives are worth weighing, and none is right for every household.
- Keep only your own employer plan and drop the spouse's plan. Some employers charge a surcharge or limit spouse enrollment when the spouse has other job coverage, so check the plan's rules first.
- Move the whole family onto one spouse's plan and decline the other employer plan, if the combined premium and out-of-pocket maximum are lower. Check your employer's rules on mid-year changes and qualifying life events.
- Keep a Marketplace plan and decline job coverage that is not affordable. If the employer plan is unaffordable or lacks minimum value, you may still qualify for the premium tax credit, and healthcare.gov lets you check by applying.
- Keep COBRA only if the active plan leaves a real gap. COBRA is secondary to a current job plan, and you can usually drop it later, but missing the window to enroll in another plan has a cost.
- Use a special enrollment period after losing coverage. A job loss or divorce opens a window to join a spouse's plan or a Marketplace plan, generally within 60 days for the Marketplace and 30 days for many employer plans.
How to find out which plan is primary and fix a denied claim
The fastest way to confirm the order is to call the member services number on the back of each insurance card and ask which plan the insurer considers primary for you or your child, and why. Write down the date, the representative, and the answer. Open enrollment for 2027 Marketplace coverage starts November 1, 2026, and HealthCare.gov lists the current deadlines, so check them before you change a plan. A claim denied for coordination reasons is usually fixed by updating the other-insurance record, not by an appeal.
Frequently Asked Questions
Which insurance is primary when my spouse and I each have an employer plan?
Your own employer plan is primary for you, and your spouse's plan is secondary, because the plan covering you as the employee pays before a plan covering you as a dependent. The same is true in reverse for your spouse. Under the NAIC model regulation used in most states for 2026 and 2027, each person's own plan comes first. Confirm with both insurers, since self-funded plans can have their own terms.
What is the birthday rule for health insurance?
The birthday rule decides the primary plan for a child covered by both married parents' plans. The plan of the parent whose birthday falls earlier in the calendar year pays first, using only month and day, not the year of birth. If the parents share a birthday, the plan that has covered a parent longer is primary. The NAIC model regulation sets the rule, and most states and insurers apply it in 2026 and 2027.
Which plan pays first for a child of divorced parents?
A court decree comes first. If it makes one parent responsible for the child's health coverage, that parent's plan is primary. If it makes both parents responsible or gives joint custody without naming one, the birthday rule applies. With no decree, the order is the custodial parent's plan, that parent's spouse's plan, the non-custodial parent's plan, then that parent's spouse's plan. Send the decree to each insurer.
Does COBRA pay before or after my new employer plan?
COBRA is secondary. Under the NAIC model regulation, coverage through a current job or as a dependent of a current employee pays before COBRA or state continuation coverage. If you start a new job with health coverage, the new plan is generally primary and COBRA pays second. Because COBRA premiums are often high, compare its cost with the benefit before keeping it, and check the deadline to drop it.
If I have a Marketplace plan and a spouse's plan, which pays first?
The answer depends on the two contracts, because individual Marketplace policies write their own coordination terms. The bigger issue is the subsidy: the IRS says enrolling in an employer plan that counts as minimum essential coverage makes you ineligible for the premium tax credit on your own Marketplace plan. Ask both insurers for the order in writing and check HealthCare.gov before keeping both.
Can an insurer deny me because I already have other coverage?
No. An ACA-compliant plan cannot turn you away or charge more because of a preexisting condition, and having other insurance is not a reason to refuse enrollment. What the second insurer can do is pay as the secondary plan, so it may cover less of a claim than you expect. Employer plans may also set rules about spouse enrollment, such as a surcharge, so read the plan's enrollment terms.
What should I do if my claim is denied because of coordination of benefits?
Call the insurer that denied the claim and ask what other-insurance information is missing. Most denials are fixed by giving the insurer the other plan's name, member ID, and policyholder details, or by returning its coordination questionnaire. Then ask the provider to bill the primary plan first and resubmit the claim to the secondary plan with the primary plan's explanation of benefits. Appeal only if the insurer still refuses after the record is updated.
Does Medicare or Medicaid change who pays first?
Yes. Medicaid and CHIP are generally the payer of last resort, so any employer plan pays first. For Medicare based on disability, Medicare.gov says a current-employment group plan from an employer with 100 or more employees pays first, and Medicare pays first below 100 employees. For people 65 and older, the cutoff is 20 employees. See the separate Medicare coordination of benefits guide for the full list.
