What is the difference between IOP and PHP billing?

PHP (partial hospitalization) is a higher, more intensive level of care than IOP (intensive outpatient), and the two are billed with different codes and reimbursement structures. Both are commonly billed per-diem (a single daily rate) rather than per individual service, though arrangements vary by payer.

What codes are used for IOP and PHP billing?

Usage varies by payer and setting. Many programs bill IOP with HCPCS codes such as H0015 (or S9480 for psychiatric IOP) and use facility revenue codes for IOP and PHP. Some payers require specific revenue codes and per-diem structures. Always confirm the exact codes with each payer.

Why do IOP and PHP claims get denied?

The most common reasons are missing or expired authorization, failure to complete concurrent review for continued stay, level-of-care downgrades, and medical-necessity documentation that doesn't meet criteria such as ASAM. Most of these are preventable.

Specialty · June 15, 2026 · 6 min read

IOP & PHP Billing: A Guide for Treatment Programs

Intensive outpatient (IOP) and partial hospitalization (PHP) programs are where a lot of behavioral health revenue, and a lot of denials, live. The billing is different from standard outpatient, and small mistakes are expensive at a per-diem rate.

IOP vs. PHP

PHP is the higher, more intensive level of care; IOP is a step down. They use different codes and reimbursement structures, and both are frequently billed per-diem, a single daily rate covering the day's services, rather than per individual service. Some payers and settings use fee-for-service or facility billing instead.

Codes and structures

Exact codes vary by payer and setting, so confirm each. In practice, programs commonly use:

Level	Commonly used	Notes
IOP	H0015 (SUD IOP); S9480 (psychiatric IOP)	Often per-diem; some payers require revenue codes
PHP	Facility revenue codes; per-diem rates	Higher intensity than IOP; stricter medical necessity

Codes and requirements differ by payer (commercial, Medicaid, Medicare) and state, always verify.

The three denial traps

Authorization. IOP/PHP almost always require prior authorization, and continued stay requires concurrent review. Miss the review window and the days deny.
Level-of-care downgrades. Payers may approve a lower level than billed; documentation has to justify the intensity.
Medical necessity. Notes must map to criteria like ASAM (for SUD) or the payer's behavioral health guidelines.

Getting paid at a per-diem rate

Because IOP/PHP reimburses per day, a single missed authorization or late concurrent review can wipe out a week of revenue. The defense is tracking every authorization and review deadline and scrubbing claims before they go out, which is where an AI addiction & SUD billing specialist earns its keep, as part of broader AI behavioral health billing. See also prior authorization for behavioral health and AI denial management.

If you're weighing outside billing help for these levels of care, see substance abuse billing services.

Protect your per-diem revenue.

See how Stable tracks authorizations and scrubs IOP/PHP claims before they deny.

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