Coordination of benefits (COB) in dental billing
Coordination of benefits (COB) is how two dental plans covering the same patient share a claim. One plan is primary and pays first under its own terms. The secondary plan then gets the claim with the primary’s payment details and pays some or all of what is left, depending on its COB rule. The patient owes whatever both plans leave.
Also calledCOBDual coverageSecondary insuranceBirthday rule
By Dr. Maya Arnaout, DDS, VP of RevenuePublished 4 min read
What is coordination of benefits?
A patient can be covered by two dental plans: their own through work and a spouse’s, or, for a child, both parents’ plans. COB is the set of rules, written into each plan, that stops the two from paying twice for the same procedure. One plan pays first as primary; the other pays second as secondary.
The order matters. Send the claim to the wrong plan first and it comes back unpaid, often with reason code 22, “this care may be covered by another payer per coordination of benefits”, while the clock on timely filing keeps running.
Which plan is primary?
Most plans follow the same order of rules. The first rule that applies decides it:
- A plan that covers the patient as the employee or subscriber is primary over a plan that covers them as a dependent.
- For a child covered by both parents, the birthday rule applies: the plan of the parent whose birthday comes first in the calendar year is primary. Only the month and day count, not the year.
- If both parents share a birthday, the plan that has covered its parent longer is primary.
- For parents who are divorced or separated, a court order can decide which plan is primary. Without one, the plan of the parent with custody usually comes first.
- A plan that covers the patient as an active employee comes before one that covers them as a retiree or through COBRA.
- If none of these settles it, the plan that has covered the patient longer is primary.
Ella Brooks, age 9, covered by both parents’ plans
Jordan’s birthday, March 4, comes before Sam’s, August 19, in the calendar year.
- Jordan BrooksPrimary
Born March 4, 1988
Sample Dental Plan A - Sam BrooksSecondary
Born August 19, 1985
Sample Dental Plan B
Sam is older, but the year does not count. March comes before August, so Jordan’s plan pays first.
Plans can word these rules differently, so confirm the order with both payers when you check eligibility, and record it in the PMS.
How much does the secondary plan pay?
It depends on the secondary plan’s COB rule, and dental plans use more than one:
- Standard, or traditional, COB: the secondary pays up to what it would have paid as primary, limited to what is still left. The patient often owes little or nothing.
- Non-duplication, and the similar carve-out method: the secondary pays only the amount by which its own normal benefit exceeds what the primary paid. If the primary paid as much or more, the secondary pays nothing.
Ella Brooks · D2391 one-surface back tooth filling
- Office fee$180.00
- Contractual write-off-$60.00
- Allowed by both plans$120.00
- Primary pays 80%$96.00
Left after the primary: $24.00. What the secondary pays depends on its rule.
Secondary uses standard COB
- Primary plan
- $96.00
- Secondary plan
- $24.00
- Patient owes
- $0.00
It pays what is left, up to its own normal benefit of $96.00.
Secondary uses non-duplication
- Primary plan
- $96.00
- Secondary plan
- $0.00
- Patient owes
- $24.00
Its normal benefit, $96.00, minus the $96.00 the primary paid, is nothing.
Both plans allow $120.00 and pay 80%. On the secondary’s ERA, what the primary already paid usually shows as OA-23.
Each plan also applies its own deductible, frequency limits and annual maximum, and the secondary pays only for procedures it covers.
How does the secondary EOB get posted?
In two passes, one per plan, against the same procedures:
- Post the primary EOB or ERA first: the payment, the contractual write-off and the patient portion. Do not bill the patient yet.
- Send the secondary claim with the primary’s payment details: the primary EOB attached to a paper claim, or the primary’s amounts in the electronic claim.
- When the secondary pays, post it as its own insurance payment against the same procedure lines. On its ERA, the amount the primary already covered usually shows as
OA-23, “the impact of prior payer(s) adjudication”. - Bill the patient only what is left after both plans.
The common mistakes: billing the patient from the primary EOB before the secondary pays, posting the secondary payment as a second primary payment, and never sending the secondary claim at all, which leaves the balance sitting in A/R.
How ScoutIQ handles it
ScoutIQ reads the primary and the secondary EOB or ERA, however each one arrives, and posts each payment, write-off and patient portion to the claim lines in your PMS. Lines it is unsure about go to a person, and denials, COB denials included, go to their own queue with the payer’s reason. ScoutIQ does not submit claims, so secondary claims go out through your PMS and clearinghouse as they do today.
Insurance Billing Automation
ERAs and EOBs read; EFT, check and card payments reconciled.
See Insurance Billing Automation