Billing · Updated 2026-09-08 · 6 min read

What is the difference between MAC and UCR in dental insurance?

One federal plan's own brochures show the switch: an 80th-percentile out-of-network allowance in 2021, the in-network fee schedule in 2026 — and the patient absorbed the difference.

A usual, customary and reasonable allowance is a percentile of what dentists in an area charge. A maximum allowable charge is a fee schedule — a fixed list, usually the carrier's own in-network one. The two produce very different patient balances on the same claim, and a plan can move from one to the other between plan years without the office noticing. MetLife's federal dental plan is a documented example in the carrier's own public brochures: its High Option paid out-of-network at "the 80th percentile of our usual and customary charges" in 2021, and by 2026 the out-of-network plan allowance on that programme was the in-network one. Out of network, 64.2% of the claim lines we measured in the twelve months to August 2026 came back allowed at or above the fee the office billed — which means those remittances say nothing at all about the plan's real allowance.

What we measured

Paid dental claim lines across the practices we serve, aggregated so no practice, patient or employer group is identifiable.

Two consequences follow. First, an out-of-network office trying to learn a plan's allowance from its own remittances is looking at its own fee on two lines in three. Second, even where the payer does reveal an allowance, one observation is a poor estimate of the stable answer — off by a median 16.5% — and half the plan-level cells Kaylie measured rest on exactly one observation.

What the carriers' own documents say

The 2021 definition, from a public federal brochure:

"the usual allowance for an area is the usual charge made by most dentists in the same geographic area for the same or similar service or supply… We use the 80th percentile charge to establish a customary allowance… payment for charges far in excess of the prevailing fee will be reduced to the 80th percentile amount for benefit payment purposes."

— The MetLife Federal Dental Plan 2021 brochure, which names the option that basis belonged to: "The High Option Plan Allowance for Out-of-Network services will be based on the 80th percentile of our usual and customary charges." The same document gives the arithmetic: sort one hundred charges for the same service lowest to highest and number them 1 to 100; the 80th percentile is the charge greater than or equal to charge number 80.

The 2026 replacement, in the same programme:

"The Plan Allowance for Out-of-Network services will be equal to the In-Network Plan Allowance for the covered service… When you use an Out-of-Network provider, you are responsible for the difference between the Plan Allowance and our payment plus the difference between the amount the provider bills and the Plan Allowance."

— The MetLife Federal Dental Plan 2026 FEDVIP brochure. The percentile is gone. The out-of-network allowance is now the in-network fee schedule, and the patient owes both gaps.

Delta explains what a percentile actually is, in a post written for brokers:

"Percentiles are calculated by ranking a set of given fees from lowest to highest. On a list of 10 given fees, the eighth ranked fee would be considered the 80th percentile."

"At the 80th percentile, 80% of dentists' fees are paid as billed. Dentists whose fees are above this percentile are charging more than most dentists in their market."

— Delta Dental, out-of-network reimbursement post, Insider Update, August 16 2022.

The same post carries Delta's own illustrative arithmetic. A PPO contracted fee of $600 at 50% coverage leaves the member paying $300; the same procedure at a non-Delta dentist billing $1,000, against an out-of-network allowance at the 90th percentile of $925, has the plan paying $463 and the member $538.

Other carriers name a third-party benchmark instead of their own claim history. A Nevada commercial PPO pays out-of-network at "the lesser of the submitted charge or the Regional Usual & Customary Rate as defined by the 80th percentile of MDR (Medical Data Research) fee [schedule] published by FAIR Health" — Liberty Dental Plan of Nevada Elite PPO Benefit Plan Summary. The 2026 BCBS FEP Dental brochure names FAIR Health for its out-of-network plan allowance and does not state a percentile at all; do not assume one.

Why it depends on the plan

Neither the method nor the percentile is a carrier constant. Delta's non-participating allowance is often a percentile of a market fee schedule chosen by the employer, anywhere across the 50th to 90th; Cigna's maximum reimbursable charge has been observed at the 80th, 85th and 90th percentile on different employers' plans. And on some products the out-of-network basis is not a percentile in the first place: Blue Shield of California's pediatric dental FAQ states that its out-of-network "reimbursement[ ]schedule is an MAC (Maximum Allowable Charge) schedule… the same MAC schedule as our small business dental PPO MAC plans", and Cigna prices out-of-network care on its retail products off "a basic Advantage fee schedule within a specified area".

The one thing every carrier agrees on is that you cannot look the number up in advance. Delta says as much to the employers buying the plans: "Delta Dental can't predict enrollees' out-of-pocket costs when they go out of network" — Delta Dental, out-of-network reimbursement post, Insider Update, August 16 2022.

What to do

• Ask which method the plan uses before you ask for a number: a percentile of area charges, a fee schedule, or the in-network allowance. The three give different answers on the same claim.
• If the answer is a percentile, ask which percentile. It is an employer purchase, and the range across plans is wide enough to move a crown estimate by hundreds.
• Re-ask at the start of each plan year for plans you see often. A programme can move from a percentile to a fee schedule between brochures, as MetLife's federal plan did.
• Do not build an out-of-network allowance from remittances where the allowed amount equals your fee. Two out-of-network lines in three are that.
• Quote the patient the coinsurance gap and the balance-billing gap as two separate numbers. On a plan paying the in-network allowance out of network, both are theirs.

Numbers last refreshed August 2026.

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