CMS-1500 · Box 33

Billing provider info (33 with 33a / 33b).

What goes here

Billing entity name + mailing address (street including a nine-digit ZIP) + a payer-facing phone number. 33a = billing NPI. 33b = other biller IDs as required by the payer.

Common mistakes

The nine-digit ZIP is missing. The phone on file routes to a patient line. PO Box only — some payers require a street address for the biller.