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Fonteum Data GlossaryPayer

What is balance billing?

Balance billing is when an out-of-network provider bills the patient for the difference between the provider's charge and what the insurer paid — the 'balance.' The No Surprises Act prohibits it for emergency services, air ambulance transport, and non-emergency care at in-network facilities without prior informed choice; Medicare and Medicaid have long-standing limits of their own.

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Full name: Balance Billing / Surprise Billing

Short explanation

Balance billing is the practice by which an out-of-network provider bills a patient for the difference between the provider's charge and the amount the patient's insurer pays — the 'balance'. The No Surprises Act prohibits balance billing in specified circumstances: emergency services, air ambulance transport, and non-emergency services at in-network facilities when the patient had no prior informed choice of provider. Medicare and Medicaid programs have long-standing limits on provider balance billing.

Last updated: 2026-07-11Reviewed by: Dr. Jennifer Montecillo, MDGullas College of Medicine, 2019. Non-practicing medical reviewer.

How it’s used

  • CMS NPPES NPI Registry: provider network status — derived from NPPES data and supplemented by insurer MRF directory data — is a key input in balance-billing compliance determinations.
  • No Surprises Act: the NSA prohibits balance billing for emergency and specified out-of-network services, the statutory boundary Fonteum's surprise-billing compliance research applies.
  • Insurer machine-readable files (Transparency in Coverage Rule): payer MRFs publish in-network rates that determine when a patient bill crosses into prohibited balance billing.

Frequently asked questions

What is balance billing?
Balance billing occurs when an out-of-network provider charges a patient for the difference between their billed rate and what the patient's insurer paid.
Is balance billing legal?
In many circumstances it is now prohibited under the No Surprises Act for emergency services, air ambulance, and unplanned out-of-network care at in-network facilities.
What is the difference between balance billing and surprise billing?
Surprise billing refers specifically to unexpected balance bills received after the fact — typically after emergency or inadvertent out-of-network care.

What’s on file, by the numbers

Platform snapshot · 2026-08-30

13.4Mproviders & companiesProviders, organizations, owners, and facilities on file
26.2Msource-linked factsSource-linked field facts in the dated platform snapshot
90sources with dataDistinct snapshot source IDs with at least one positive record count
16fresh sourcesDistinct source IDs whose latest positive-data snapshot falls within the preceding 45 days
111sources integratedActive registry rows; integration does not establish a load
13state Medicaid jurisdictionsDistinct states represented in the state-exclusions serving table

Integrated, with-data, and fresh-observation counts are separate. No platform-wide source-completeness count is published. Completeness is source-specific and must be evaluated against the named source's expected scope. State coverage is a separate jurisdiction measure.

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Named medical review

Reviewed by Jennifer Montecillo, MD, medical reviewer. Non-practicing medical reviewer.

Read the full provenance and attestation methodology →

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