CPT Code 99357: Prolonged inpatient service, each additional 30 min

When to Use CPT 99357

Use CPT code 99357 when billing for prolonged inpatient service, each additional 30 min. This code is used by licensed therapists (LCSW, LPC, MFT, Psychologist) for outpatient sessions.

Adding CPT 99357 to a Superbill

When generating a superbill with CPT 99357, include the ICD-10 diagnosis code, date of service, fee charged, amount paid, and your NPI number. Superbilled pre-fills common therapy CPT codes automatically.

Common ICD-10 Pairings

These diagnosis codes are frequently used alongside CPT 99357:

Documentation Requirements

Document each additional 30-minute increment of prolonged inpatient time and clinical justification for continued extended care.

Common Denial Reasons

• ✗ Billed without 99356 as the primary prolonged inpatient code
• ✗ Additional time not documented or justified
• ✗ Total prolonged time exceeds reasonable clinical need

Got one of these on a remittance? Decode the denial code.

Modifier Notes

Add-on code — must be billed with 99356.

Reimbursement Expectations

OON reimbursement typically 45-60% of UCR. Expect $23-$60 per additional 30 minutes.