When a patient has two dental plans, how much does each plan pay and what does the patient owe?

When a patient has two dental plans, the primary plan pays first under its own terms, as if no other coverage existed. Under traditional coordination of benefits, the secondary then pays the balance of the allowed amount the primary left unpaid — up to what the secondary would have paid on its own — which often brings the patient share of the allowed charge to $0. Under a non-duplication clause, the secondary pays only the amount by which its own benefit exceeds the primary's payment, which is frequently $0 when both plans cover the service at the same percentage. Which plan is primary comes from the state's adopted version of the NAIC Coordination of Benefits Model Regulation; the non-duplication method itself is a plan-document term the model regulation does not define, so the plan document controls it — and a self-funded employer plan is generally governed by ERISA rather than the state's COB rules, though not categorically: a self-funded governmental or church plan is not an ERISA plan at all.

Why can the secondary dental plan pay $0?

The common reasons: a non-duplication clause (the secondary's own benefit does not exceed what the primary paid), an exhausted secondary annual maximum, a service the secondary plan does not cover, or frequency, waiting-period, or documentation rules that block payment. The calculator on this page models the first two; the others require the plan documents.

Do coordination-of-benefits rules even apply to dental plans?

Yes. The NAIC Coordination of Benefits Model Regulation defines a "plan" to include group and non-group insurance contracts and subscriber contracts that pay or reimburse the cost of dental care, so the model's order-of-benefits rules reach dental benefits rather than stopping at medical. Two limits travel with that: the model binds only as each state adopts and amends it, and a self-funded employer (ERISA) plan sets its own order in the plan document.

Billing & claims · Last verified 2026-08-30

Dental coordination of benefits

One plan pays first; the second coordinates on what is left of the allowed amount. Enter the claim numbers below to estimate each plan's payment and the patient share.

Estimate the two-plan split

Use the numbers from the treatment estimate, EOB, or carrier portal. The estimate updates as you type.

Billed feeThe office's submitted fee, in dollars.Allowed amountThe contracted amount both plans recognize — never more than the fee.Primary coverage %The primary plan's percentage for this procedure category.Secondary coverage %The secondary plan's percentage for the same category.

Secondary plan's coordination method

Traditional (standard) COBSecondary pays the remaining allowed balance, capped by its own benefit.Non-duplicationSecondary pays only the excess of its own benefit over what primary paid.

Maintenance-of-benefits and carve-out plans are not modeled here. Their reductions are defined by each plan document rather than a single published formula, so read the plan's COB provision — or ask the carrier which method it applies — instead of estimating.

Add deductibles and annual maximums

Primary deductible left$0 if waived or already met.Secondary deductible leftOnly the part that applies to this service.Primary annual max leftSecondary annual max left

Estimated patient portion

The two plans together cover the full allowed amount in this estimate — the patient shows $0 of the allowed charge.

Primary pays: $128
Secondary pays: $32
Plans total: $160
Office write-off: $40

How we calculate this

Each plan's standalone benefit is its coverage percentage applied to the allowed amount after its remaining deductible, capped by its remaining annual maximum. The primary pays its standalone benefit. Traditional COB: secondary = min(secondary standalone, allowed − primary paid). Non-duplication: secondary = max(0, secondary standalone − primary paid), never more than the remaining balance.

Both plans are treated as recognizing one allowed amount; in practice each plan may apply its own allowable, which changes the arithmetic. Method definitions follow the NAIC Coordination of Benefits Model Regulation framework and the ADA's COB guidance, linked in the sources on this page (last verified 2026-08-30). Frequency limits, waiting periods, alternate benefits, and documentation rules are not modeled — treat this as an estimate for the patient conversation, not a coverage determination.

Nothing you type here leaves your browser — the results are computed locally on this page.

Primary plan

Pays first, under its own terms, as if no other plan existed.

Traditional COB

Secondary pays the remaining allowed balance, capped by its own benefit.

Non-duplication

Secondary pays only its excess over the primary — often $0.

ERISA plans

Self-funded plans are generally outside state COB rules (29 U.S.C. § 1144).

Traditional COB vs non-duplication: worked examples

Each plan's standalone benefit is its coverage percentage applied to the allowed amount after its deductible, capped by its annual maximum. All examples use a $200 fee and $160 allowed amount unless noted.

Example	Primary pays	Secondary pays	Patient	What it shows
Traditional, both plans at 80%	$128	$32	$0	On a $160 allowed amount, the primary pays $128 (80%) and traditional COB lets the secondary pick up the remaining $32.
Non-duplication, both plans at 80%	$128	$0	$32	Same claim, but the secondary's own benefit ($128) does not exceed what the primary paid ($128), so it pays $0 and the patient owes $32.
Non-duplication, richer secondary (50% / 80%)	$80	$48	$32	The secondary pays only its excess over the primary: $128 − $80 = $48. Non-duplication still leaves the 20% neither plan covers.
Traditional, $50 primary deductible left	$88	$72	$0	The primary pays 80% of $110 after its deductible ($88); traditional COB lets the secondary absorb the rest, deductible included.
Traditional, secondary annual maximum used up	$128	$0	$32	A secondary with $0 of annual maximum left pays nothing under either method — the patient owes whatever the primary left.

What varies by plan and state

Which plan is primary and which method the secondary uses come from the plan documents and the state's adopted version of the NAIC model regulation. Editions and amendments differ by state, and which state adopted which edition was not verified against current state code — so this page deliberately states no per-state COB rule.
Self-funded employer plans are generally governed by ERISA rather than state insurance regulation (29 U.S.C. § 1144). Such a plan can use non-duplication or its own order-of-benefits rules even where the state's adopted COB rules say otherwise — the plan document controls. "Generally" matters: a self-funded governmental or church plan is not an ERISA plan at all, so state law can reach it.
Maintenance-of-benefits and carve-out plans are not modeled here. Their reductions are defined by each plan document rather than a single published formula, so read the plan's COB provision — or ask the carrier which method it applies — instead of estimating.
The calculator treats both plans as recognizing one allowed amount. In practice each plan may apply its own allowable or fee schedule, which changes the arithmetic.

Which plan is primary for a child?

The birthday rule: the parent whose birthday falls earlier in the calendar year — month and day only — holds the primary plan. Check a specific case on the birthday-rule page, including the same-day tie-break and the court-decree exception.

Common questions

Why can the secondary dental plan pay $0?: The common reasons: a non-duplication clause (the secondary's own benefit does not exceed what the primary paid), an exhausted secondary annual maximum, a service the secondary plan does not cover, or frequency, waiting-period, or documentation rules that block payment. The calculator on this page models the first two; the others require the plan documents.
Does the calculator handle maintenance-of-benefits or carve-out plans?: No. Maintenance-of-benefits and carve-out plans are not modeled here. Their reductions are defined by each plan document rather than a single published formula, so read the plan's COB provision — or ask the carrier which method it applies — instead of estimating.
Do coordination-of-benefits rules even apply to dental plans?: Yes. The NAIC Coordination of Benefits Model Regulation defines a "plan" to include group and non-group insurance contracts and subscriber contracts that pay or reimburse the cost of dental care, so the model's order-of-benefits rules reach dental benefits rather than stopping at medical. Two limits travel with that: the model binds only as each state adopts and amends it, and a self-funded employer (ERISA) plan sets its own order in the plan document.

Sources

NAIC Coordination of Benefits Model Regulation (MDL-120) — Model order-of-benefit-determination rules most states adopt, including the birthday rule, the longer-coverage tie-break, and court-decree sequencing.
NAIC model laws index — Where NAIC publishes current model text and state-adoption information. This cluster states no per-state COB rule, so no adoption row is published here.
29 U.S.C. § 1144 — ERISA preemption of state law — Why a self-funded employer plan is generally governed by ERISA rather than a state's COB rules, and can follow its own coordination method and order of benefits. The section never uses the words self-funded; the rule comes from the courts reading its preemption, saving, and deemer clauses together.
ADA guidance on coordination of benefits — Practice-facing definitions of traditional COB, non-duplication, and the maintenance-of-benefits variants this calculator declines to model.

The full claim cycle, in order

Verification, documentation requirements, denial codes, and prompt-pay deadlines sit alongside this COB reference on one free hub, organized the way a claim moves.

Open the dental billing hub