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Who Pays First? Primary vs Secondary Insurance

When a patient has more than one source of coverage, one payer processes the claim first and the other picks up what is left. This page answers three questions: which coverage generally pays first, what still has to be verified, and what to do with the secondary claim. Every rule below is linked to the federal regulation, CMS manual or official page it comes from.

  • 3 toolsPayer-order finder and two calculators
  • 14 coverage combinationsEach with the rule behind it
  • Every rule citedFederal regulations and CMS manuals
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Written by CureAdvantage from primary sources. Federal rules were read on eCFR and govinfo, Medicare rules in CMS manuals and on Medicare.gov, and the dependent-child rules from an enacted state regulation. Sources checked September 22, 2026. This is general information about payer order, not legal, coverage or payment advice for a specific patient.

Who Pays First?

Answer as much as you know. The finder shows the payer order the rules generally produce, the facts that could change it, and what to do next on the claim. When a fact that decides the answer is missing, it says so instead of guessing.

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Who Pays First?

Coordination of benefits for Medicare, Medicaid, TRICARE, VA, employer plans, COBRA, accident coverage and children with two plans.

This finder needs JavaScript. Every rule it applies is written out below in the Medicare Secondary Payer section and the coverage combination cards.

How Coordination of Benefits Works

Coordination of benefits decides the order in which payers process a claim when someone has more than one source of coverage. The primary payer processes the claim as though no other coverage existed. The secondary payer then considers what is left, within the limits of its own contract or, for Medicare, within the limits federal regulation sets.

Three different bodies of rules are at work, and they are not interchangeable:

  • Medicare Secondary Payer (MSP) rules are federal. They are written in statute and in 42 CFR part 411, and they decide when Medicare pays second.
  • State coordination rules govern insured health plans a state regulates. They contain the familiar order-of-benefit provisions, including the birthday rule for dependent children.
  • Program rules apply to Medicaid, TRICARE, VA care and the Indian Health Service. Each program has its own statute or regulation, and these do not follow the commercial order-of-benefit rules.

Two practical consequences follow. First, a rule that is true for one of these does not automatically carry over to the others. Second, the coordination record itself matters as much as the rule: payers hold their own view of who is primary, and a claim will deny if that record disagrees with the claim, even where the rule is on your side.

Medicare Secondary Payer Rules

Medicare pays second only in the situations federal law defines. The three group health plan situations turn on why the patient has Medicare.

Age-based Medicare and a current employer plan

Rule
The group health plan pays first where the patient is 65 or older, is covered by the plan by virtue of current employment status (their own or a spouse’s), and the employer has 20 or more employees. Below that size, Medicare pays first.
Watch for
A multi-employer plan counts if at least one participating employer meets the 20-employee test, and such a plan may request an exception for small employers. Refusing the employer’s plan makes Medicare primary.
Source
42 CFR 411.172

Disability-based Medicare and a large group health plan

Rule
Where the patient has Medicare because of disability and is covered through current employment (their own or a family member’s) under a large group health plan, the plan pays first. A large group health plan is one covering an employer that employed at least 100 employees on half or more of its business days in the previous year.
Watch for
If the patient also has ESRD, the ESRD rule applies instead.
Source
42 CFR 411.101, 42 CFR 411.206

ESRD-based Medicare

Rule
During a 30-month coordination period the group health plan pays first, regardless of the employer’s size and regardless of whether anyone has current employment status. COBRA and retiree coverage are included.
Watch for
If Medicare was already properly primary before ESRD eligibility began, it stays primary. A new period of ESRD eligibility starts a new 30 months.
Source
42 U.S.C. 1395y(b)(1)(C), MSP Manual ch. 2 §20

What “current employment status” means

Rule
A patient has current employment status when actively working, when they are the employer, or when they are not working but keep employment rights in defined circumstances. COBRA continuation is specifically excluded, and so is coverage held purely as a retiree.
Why it matters
This single definition decides most Medicare questions: no current employment status means the working-aged and disability rules do not apply, so Medicare pays first.
Source
42 CFR 411.104

Two further points apply across all three situations. A group health plan may not take Medicare entitlement into account or pay secondary simply because its contract says so: federal law makes Medicare secondary regardless of what the plan document states. And where a plan denies or will not pay promptly, Medicare may make a conditional payment that has to be repaid once the other payer pays.

Common Coverage Combinations

These cards summarise the combinations that come up most often. They describe the general rule; the facts listed under “what can change it” are the ones worth confirming before the claim goes out.

1. Medicare + employer coverage (still working)

Generally primary
The group health plan, where the employer meets the size test (20+ for age, 100+ for disability).
Generally secondary
Medicare.
Why
The MSP working-aged and disability provisions bar those plans from taking Medicare entitlement into account.
What can change it
Employer size; whether coverage is really by virtue of current employment; a refused plan; multi-employer exceptions; ESRD.
Source
42 CFR 411.172, 411.206

2. Medicare + COBRA

Generally primary
Medicare.
Generally secondary
COBRA continuation coverage, to whatever extent it pays.
Why
COBRA continuation is not coverage by virtue of current employment status, so the working-aged and disability rules do not apply.
What can change it
ESRD-based Medicare reverses this during the 30-month coordination period. Medicare.gov also warns that COBRA may pay very little once Medicare is primary.
Source
42 CFR 411.104, Medicare.gov

3. Medicare + Medicaid

Generally primary
Medicare.
Generally secondary
Medicaid, which pays last.
Why
Medicaid is the payer of last resort, and Medicare.gov states that Medicaid never pays first for services Medicare covers.
What can change it
Where there is a third coverage, Medicaid still pays after it. State programs set their own enrollment and crossover requirements.
Source
Medicaid.gov COB/TPL, 42 CFR 433.139

4. Medicare + retiree coverage

Generally primary
Medicare.
Generally secondary
The retiree plan.
Why
Retiree coverage is not coverage by virtue of current employment status.
What can change it
ESRD during the coordination period. A reemployed retiree who qualifies for coverage through renewed work is treated as currently employed. Retiree plans often require both Part A and Part B.
Source
42 CFR 411.172(d), Medicare.gov

5. Medicare + TRICARE

Generally primary
Medicare, for a patient who is not on active duty. For an active duty service member, TRICARE pays first.
Generally secondary
TRICARE (TRICARE For Life) for the non-active-duty patient.
Why
The TRICARE regulation states that where a beneficiary is eligible for both, Medicare is the primary payer, with an exception for retroactive disability determinations; Medicare.gov describes the active duty reversal.
What can change it
Care in a military hospital or clinic, services TRICARE covers but Medicare does not, and Part D drug coordination all follow different paths.
Source
32 CFR 199.8(d), Medicare.gov

6. Medicare + VA benefits

Generally primary
Neither, in the usual sense: the patient chooses which benefit to use for each episode of care.
Generally secondary
Not applicable — the two programs generally cannot pay for the same item or service.
Why
Medicare pays for Medicare-covered care; the VA pays for VA-authorized care. Medicare does not pay for services paid for by another government entity.
What can change it
If the VA authorised only part of a non-VA hospital stay, Medicare may cover the services the VA did not authorise. Authorisation must be arranged before the care.
Source
Medicare.gov, 42 CFR 411.8

7. Medicare + workers’ compensation

Generally primary
Workers’ compensation, for care related to the work injury or illness.
Generally secondary
Medicare, and only in limited circumstances.
Why
Medicare does not pay for services for which payment has been made, or can reasonably be expected to be made, under workers’ compensation.
What can change it
A denied or disputed claim, or a carrier that will not pay promptly, can support a conditional Medicare payment that must later be repaid. Unrelated care is billed normally.
Source
42 CFR 411.40, 411.45

8. Medicare + liability or no-fault insurance

Generally primary
The no-fault or liability insurer, for services related to the accident or injury.
Generally secondary
Medicare.
Why
Medicare is secondary to no-fault and liability insurance for accident-related care, including personal injury protection and medical payments coverage.
What can change it
Which services are accident-related; whether the insurer pays promptly, which CMS defines as 120 days for liability; and any settlement, which can require repayment.
Source
42 CFR 411.50, 411.52

9. Child covered by both parents (parents together)

Generally primary
The plan of the parent whose birthday falls earlier in the calendar year, using month and day only.
Generally secondary
The other parent’s plan. If both parents share a birthday, the plan that has covered its parent longer pays first.
Why
This is the order-of-benefit provision states have enacted for dependent children whose parents are married or living together.
What can change it
Which state’s rules apply; whether a plan is self-funded and uses its own provision; whether the child has coverage of their own.
Source
28 Tex. Admin. Code §3.3507 (example of an enacted rule)

10. Child of divorced or separated parents

Generally primary
With no court order allocating responsibility: the custodial parent’s plan, then that parent’s spouse, then the non-custodial parent, then their spouse.
Generally secondary
The next plan in that sequence.
Why
The enacted order-of-benefit rules set this sequence when no order assigns responsibility for the child’s health coverage.
What can change it
Any court order about health coverage; a change of custody; a different state’s rules.
Source
28 Tex. Admin. Code §3.3507(d)(2)

11. Court-ordered coverage for a child

Generally primary
The plan of the parent the order makes responsible for the child’s health coverage or expenses, once that plan knows about the order. If that parent has no coverage for the child but their spouse does, the spouse’s plan is primary.
Generally secondary
The other parent’s plan.
Why
The enacted rules put a court order ahead of the birthday rule, but only from the point the plan has actual knowledge of it.
What can change it
An order that names both parents, or grants joint custody without assigning health coverage, sends the question back to the birthday rule.
Source
28 Tex. Admin. Code §3.3507(d)(2)(B)

12. Own plan + spouse’s plan

Generally primary
The plan that covers the patient as the employee, member or subscriber.
Generally secondary
The plan that covers the patient as a dependent.
Why
The enacted order-of-benefit rules put non-dependent coverage ahead of dependent coverage.
What can change it
Medicare can reverse the order in defined circumstances; self-funded plans follow their own provision; state rules vary.
Source
28 Tex. Admin. Code §3.3507(d)(1)

13. Active employer plan + COBRA or state continuation

Generally primary
The plan covering the person as an active employee, or as the dependent of one.
Generally secondary
The COBRA or state continuation coverage.
Why
The enacted rules place active coverage ahead of continuation coverage, where the employee/dependent rule has not already settled the order.
What can change it
A continuation plan whose own provision conflicts; Medicare in the mix; a different state’s rules.
Source
28 Tex. Admin. Code §3.3507(d)(3)–(4)

14. Commercial coverage + Medicaid

Generally primary
The commercial or other coverage.
Generally secondary
Medicaid, which pays last.
Why
Federal rules require liable third parties to meet their obligation before Medicaid pays, and require states to identify those third parties.
What can change it
Defined exceptions to cost avoidance in federal rules; each state program’s own documentation and timing requirements.
Source
42 CFR 433.139, Medicaid.gov

ESRD 30-Month Coordination Period Calculator

When a patient has Medicare because of end-stage renal disease, the group health plan pays first for a 30-month coordination period. The period is counted in whole months from the first month of ESRD-based Medicare entitlement, or the first month the patient would have been entitled had they applied, whichever is earlier. Enter what you know and the calculator shows the arithmetic.

Free tool

ESRD 30-month coordination period

Works out the first month of ESRD-based Medicare eligibility, the coordination period, and the month Medicare generally becomes primary.

Two things this calculator will not do. It does not decide whether the patient is entitled to Medicare, which Social Security determines. And it does not apply the dual-entitlement exception automatically: if Medicare was already the correct primary payer before ESRD eligibility began, Medicare stays primary, and the coordination period does not put the plan in front.

Medicare Secondary Payment Calculator

When Medicare is the secondary payer, it does not simply pay the balance. For services paid on a fee schedule or reasonable charge basis, regulation sets three amounts and Medicare pays the lowest of them. This calculator shows all three, so the result can be checked rather than trusted.

Free tool

Medicare secondary payment

The three-part calculation in 42 CFR 411.33(a), for services Medicare pays on a fee schedule or reasonable charge basis.

Only if it is lower than the charge.
Leave blank to work it out from the two fields below.
Enter the percentage that applies to this service; do not assume one.

What this calculator does not cover. Services Medicare pays on another basis, such as inpatient hospital claims, use a different four-part calculation in the same regulation. Medicare Advantage plans are not Original Medicare and set their own coordination terms. And no secondary payment is made at all where the provider is obligated to accept, or voluntarily accepts, the primary payment as payment in full.

How to Bill the Secondary Claim

The order of payers is only half the job. This is the sequence that follows once the primary payer has processed the claim. Payer-specific fields, addresses and deadlines are deliberately not listed here, because they differ by payer and change.

  1. Read the primary remittance advice or EOB in full. Record the allowed amount, the paid amount, the contractual adjustment, patient cost sharing and anything denied. Those figures, not the charge, drive the secondary claim.
  2. Separate what was denied from what was simply not paid. A service the primary denied for medical necessity or coverage is a different problem from a balance left after normal cost sharing, and the secondary payer will treat it differently.
  3. Check whether the secondary payer receives the claim automatically. Medicare has a crossover process that forwards claims to supplemental and other payers that have an agreement in place. Where crossover applies, submitting a second claim yourself can create a duplicate.
  4. Confirm the coordination record before you send anything. If the secondary payer’s record does not show the correct primary coverage, the claim will deny no matter how it is coded. Updating that record is often something only the patient can do.
  5. Build the secondary claim with the primary payer’s adjudication information. For Medicare as secondary, CMS’s instructions require the primary payer’s allowed, paid and denied amounts on the claim, with the primary payer’s EOB or remittance advice attached to a paper claim.
  6. Put the other coverage in the fields the payer expects. CMS’s MSP instructions identify the primary insurance in the insured items of the CMS-1500 rather than the item Medicare reserves for Medigap, and the accident-related items must be completed where they apply.
  7. Check the payer’s own requirements before submitting. Attachment format, whether the claim goes electronically, and the filing window are all payer-specific. Confirm them rather than carrying assumptions from one payer to another.
  8. Submit and record what was sent. Keep the claim, the primary remittance advice and the date, so a later timely filing or duplicate question can be answered with evidence.
  9. Reconcile the secondary response. Compare the secondary payment against what the rules permit. For Medicare as secondary, the calculator above shows the three amounts; for other payers, the plan’s coordination provision governs.
  10. Work out any remaining patient balance carefully. Contractual adjustments, the primary payer’s write-offs and, for Medicare, the limit on what an assigned provider may collect all reduce what can legitimately be billed to the patient.

When a Secondary Claim Denies

Coordination-of-benefits denials usually mean the payer’s picture of the patient’s coverage does not match the claim. These are the common patterns and what to do with each. Specific denial code text is not reproduced here: those code descriptions are maintained by a standards body and are not ours to republish.

The primary payer’s information is missing from the claim

What it may mean: the claim arrived without the primary payer’s allowed, paid or denied amounts, so the secondary payer cannot calculate anything.

What to check: whether the adjudication figures were carried into the claim, and whether the remittance advice was attached where the payer requires it.

What to do next: rebuild the claim with the primary payer’s figures and resubmit the way that payer requires for corrected or secondary claims.

The payer believes another plan should pay first

What it may mean: the payer’s coordination record puts a different payer in the primary position, or it has no record of the other coverage at all.

What to check: which payer the record shows as primary, and whether the rules on this page support that order.

What to do next: where the record is wrong, the patient usually has to correct it with their own plan. For Medicare, CMS directs beneficiaries to the Benefits Coordination and Recovery Center.

The payer order on the claim was wrong

What it may mean: the claim was sent to the secondary payer first, or to the primary payer as though it were secondary.

What to check: the rule that applies to this combination, and the facts that decide it, such as employer size or current employment status.

What to do next: bill the correct primary payer first, then rebuild the secondary claim from its remittance advice.

The coverage was not active on the date of service

What it may mean: the policy ended, the patient changed jobs or plans, or continuation coverage lapsed.

What to check: the eligibility response for the date of service, not for today.

What to do next: identify the coverage that was in force on that date and rebill accordingly.

The subscriber or member details do not match

What it may mean: the patient is a dependent and the claim carries the wrong subscriber, or a name, date of birth or member number does not match the payer’s file.

What to check: the subscriber’s details on the card and in the eligibility response, and the patient’s relationship to that subscriber.

What to do next: correct the demographic and subscriber data, then resubmit.

The patient has never completed the plan’s coordination questionnaire

What it may mean: the plan is holding claims until the member confirms whether other coverage exists. This is common at the start of a plan year.

What to check: whether the payer has an outstanding request to the member.

What to do next: ask the patient to complete it. No amount of rebilling will clear this one.

The expected crossover never arrived

What it may mean: the claim was expected to be forwarded automatically to the secondary payer and was not.

What to check: whether the primary remittance advice indicates the claim was forwarded, and how long the receiving payer takes.

What to do next: where it was not forwarded, submit the secondary claim directly with the primary remittance information.

The claim is treated as a duplicate

What it may mean: the same claim reached the payer twice, often because it was both crossed over and submitted manually.

What to check: the payer’s record of when each claim arrived, and whether the first is still in process.

What to do next: let the original finish rather than resubmitting again, and use the payer’s corrected-claim route if a change is genuinely needed.

The service was accident- or work-related

What it may mean: the health plan or Medicare has identified the care as related to an accident or a work injury, which changes which payer is liable.

What to check: whether an open workers’ compensation, no-fault or liability claim exists, and which services relate to it.

What to do next: bill the responsible insurer. Where that insurer denies or will not pay promptly, Medicare may make a conditional payment that has to be repaid.

The patient’s coverage changed and nobody told the payer

What it may mean: a new employer plan, a Medicaid determination, retirement or a spouse’s plan change altered the order after the last verification.

What to check: the current coverage set and the effective dates of each.

What to do next: re-verify, update the record with the payer where the patient can, and rebill in the correct order.

State Rules, Medicaid and the Limits of This Page

The dependent-child rules, the employee-over-dependent rule and the active-over-continuation rule on this page come from the order-of-benefit provisions states have enacted for the health coverage they regulate. This page cites Texas’s enacted version as a worked example, because it is public and readable. Other states have adopted similar provisions, but the wording and the scope are not identical everywhere, and the rules reach only the kinds of coverage the state regulation lists. A self-funded employer plan follows the coordination provision in its own plan document.

Medicaid is different again. Federal rules make it the payer of last resort: states must identify liable third parties and those third parties must meet their obligation before Medicaid pays. What that looks like on a claim, including documentation and timing, is set by each state programme, so the state’s own manual is the authority for anything more specific. This page does not attempt a fifty-state Medicaid decision tree, and any state-specific question should be confirmed in that programme’s own materials.

Medicare Advantage plans are also outside the calculations here. They are Medicare-approved plans with their own coordination terms, and a question about one should go to the plan.

Common Questions

How do I know which insurance is primary?

It depends on the kind of coverage, not on which card the patient hands over. Medicare cases follow the Medicare Secondary Payer rules in federal regulation: an employer group health plan pays first for a working patient aged 65 or over if the employer has 20 or more employees, and for a patient with disability-based Medicare if the employer has 100 or more employees. COBRA and retiree coverage are not current employment, so Medicare generally pays first. For two private plans, states have enacted order-of-benefit rules under which the plan covering someone as an employee comes before the plan covering that person as a dependent.

Does the birthday rule always decide which parent’s insurance is primary?

No. The birthday rule is a coordination convention states have enacted for dependent children, and it applies when the parents are married or living together, or when a court order does not make one parent responsible. Where a court order makes one parent responsible for the child’s health coverage and the plan knows about it, that parent’s plan is primary instead. The rule also does not reach every plan: a state’s coordination regulation applies only to the coverage that state regulates, and a self-funded employer plan follows its own coordination provision.

Is Medicare primary or secondary?

Both happen. Medicare pays second when a group health plan covers the patient through current employment and the employer is large enough (20 or more employees for age-based Medicare, 100 or more for disability-based Medicare), during the 30-month ESRD coordination period, and for accident or work-injury care covered by workers’ compensation, no-fault or liability insurance. Medicare pays first when the other coverage is COBRA, retiree coverage, Medicaid, or an employer plan below those employee thresholds, and for a non-active-duty patient with TRICARE.

Is Medicaid ever the primary payer?

Medicaid is the payer of last resort. Federal rules require states to identify liable third parties and require those third parties to meet their obligation before Medicaid pays, and Medicare.gov states that Medicaid never pays first for services Medicare covers. Bill the other coverage first and then the state program, with the other payer’s remittance advice.

How long is the ESRD 30-month coordination period?

Thirty consecutive months, counted from the first month the patient is entitled to Medicare Part A because of end-stage renal disease, or the first month they would have been entitled had they applied, whichever is earlier. During that period the group health plan pays first regardless of employer size and regardless of whether anyone is still working, including COBRA and retiree coverage. The regulation text still describes 12- and 18-month periods because it was never updated after the statute moved to 30 months for items and services furnished on or after August 5, 1997.

How is the Medicare secondary payment calculated?

For services Medicare pays on a fee schedule or reasonable charge basis, Medicare pays the lowest of three amounts under 42 CFR 411.33(a): the actual charge (or the amount the provider is obligated to accept as payment in full, if lower) minus the primary payment; the amount Medicare would have paid if there were no primary payer; and the higher of the Medicare fee schedule amount or the primary payer’s allowable charge, minus the primary payment. Medicare makes no secondary payment at all where the provider accepts the primary payment as payment in full.

Why did the secondary claim deny for coordination of benefits?

Usually because the payer’s record of the patient’s other coverage does not match the claim. Common causes are missing primary payer payment information, a payer that believes another plan should pay first, coverage that ended, a subscriber mismatch, an expected crossover that never arrived, or a coordination record the patient has never updated with the plan. Each of these is fixed differently: some need a corrected claim with the primary remittance information, and some need the patient to update the coordination record with their own plan before any claim will pay.

Do I bill the secondary payer with the primary EOB?

For Medicare secondary claims, CMS’s instructions require the claim to carry the primary payer’s allowed, paid and denied amounts, and a paper claim must have the primary payer’s explanation of benefits or remittance advice attached. Other payers set their own requirements, so confirm what each one expects instead of assuming a single standard.

Which insurance is primary for a child covered by both parents?

Where the parents are married or living together, the enacted state rules make the plan of the parent whose birthday falls earlier in the calendar year primary, using month and day only. If both parents share a birthday, the plan that has covered its parent longer pays first. Where the parents are separated, a court order making one parent responsible controls once the plan knows about it; with no such order the order runs through the custodial parent, that parent’s spouse, the non-custodial parent, then their spouse.

Does the patient get to choose which plan is primary?

No. Payer order follows the applicable rules and the plans’ coordination provisions, not preference. A patient can decline coverage, which changes what they have, but the order among the coverages they hold is set by rule. For Medicare, federal law also prohibits an employer plan from taking Medicare entitlement into account to push Medicare into the primary position.

Sources and Methodology

Every rule on this page comes from one of the sources below. Where a question depends on facts the tool cannot know, such as employer size or the terms of a court order, the tool says so rather than choosing an answer.

Two deliberate omissions. Denial code descriptions are not reproduced, because that code set is maintained by a standards body under its own terms. And the model coordination rules published by the association of state insurance regulators are not quoted; this page paraphrases the rules and cites a state’s enacted version instead.

Calculations were checked against the worked examples in the sources themselves: the secondary payment example in 42 CFR 411.33(b), the physician example in MSP Manual ch. 3 §10.1.2, and the ESRD coordination period examples in MSP Manual ch. 2 §20.1.3.

For filing deadlines once you know which payer is first, see the timely filing limits reference. To estimate what the patient owes after a plan processes a claim, use the patient responsibility calculator. For modifiers and liability notices on Medicare claims, see the medical billing modifiers lookup. More free references are in the free tools hub.