How Medicare billing units work
A drug's billing unit is set by its HCPCS descriptor, not by the vial. Rituximab (J9312) is defined as "injection, rituximab, 10 mg," so its billing unit is 10 mg: a 700 mg dose is 70 units. You divide the administered dose by the billing unit and round up to whole units. This tool reads the unit basis from the current CMS ASP file, so the number matches what Medicare expects.
JZ and JW: administered vs. discarded
Since July 2023, single-use-vial drugs require either JZ (attesting zero waste) or JW (reporting the discarded amount) on the claim. When the vials you must open hold more than the dose, the leftover is discarded drug: you bill the administered units with JZ and the discarded units on a separate JW line, and Medicare reimburses both. Skipping the JW line leaves money on the table. This tool draws the fewest vials that cover the dose, then splits the result into JZ and JW for you.
Frequently asked
How do I calculate Medicare billing units for a drug?
Divide the administered dose by the drug's billing unit (from the HCPCS descriptor) and round up. Rituximab (J9312) bills per 10 mg, so a 700 mg dose is 70 units. This tool does it for you and shows the math.
What are the JW and JZ modifiers?
JZ attests there was zero discarded drug; JW reports the discarded amount from a single-use vial on a separate line so Medicare reimburses the waste. Since July 2023 one of the two is required on single-use-vial drugs.
Do I bill the units I administered or the vials I opened?
You bill the units administered to the patient with JZ, and separately the units discarded from single-use vials with JW. Together they equal the units in the vials opened.
How much does Medicare pay, and what will the patient owe?
Medicare Part B pays the ASP+6% payment limit per billing unit, updated quarterly. To see the allowed amount for a specific dose, your payer's rate, and the patient's out-of-pocket with any copay assistance, run it through the cost estimator.
- Source
- Billing unit basis from the current CMS ASP Drug Pricing file; vial sizes and NDC-to-HCPCS billable units from CMS crosswalks. HCPCS J/Q codes are public domain.
- Maintained by
- Erin Rose, Founder, under CareCost's methodology and editorial policy. Corrections are logged on the Corrections page.
- Not advice
- General billing reference, not legal or billing advice. Confirm units, wastage, and modifier billing against the policy that applies to your MAC and payer.