Search the current HCPCS Level II code set by the drug's generic name, then check that the descriptor matches the drug's form and route. To go from an NDC to a J-code, use a crosswalk such as CMS's quarterly ASP NDC-HCPCS crosswalk, and confirm the match against the descriptor.
From a drug name
J-code descriptors use the generic (nonproprietary) name, so search by that rather than the brand: "pembrolizumab", not "Keytruda". Then read the whole descriptor: some drugs have separate codes for different routes, formulations or biosimilars, and the descriptor's dose amount sets the billing unit.
Med-Code's J-code directory lists codes with their descriptors and billing units, and its drug pages link a drug to its code where Med-Code's curated directory has an exact match.
From an NDC
An NDC does not contain its J-code; you need a crosswalk. CMS publishes the ASP NDC-HCPCS crosswalk each quarter, listing the NDCs it associates with each drug code for Part B payment. Payers and billing systems keep their own crosswalks too.
On Med-Code, an NDC page shows a J-code only when the product's brand or single active ingredient and its route exactly match an entry in the curated directory. Otherwise it says no code was found rather than guessing.
Checks before you bill it
Match the route: an injectable and an oral form of the same ingredient are billed differently. Match the product: biosimilars and combination products usually have their own codes. Check the date: codes change quarterly. And if the drug is self-administered, it may not be billable under a J-code at all.
Questions
What if there's no J-code for the drug?
New drugs are often billed with an unclassified code (J3490 or J3590, or C9399 in hospital outpatient settings) with the NDC, dose and often an invoice, until a specific code is assigned.