Billing code 21931: Back mass excisionMedicare rate & RVUs

Medicare pays $453.58 for 21931 nationally in a facility.

Medicare allowed amount for participating (non-QP) physicians, before deductible, coinsurance and claim adjustments. Not a patient’s bill or a hospital charge.

What 21931 covers

This service removes a soft-tissue mass located in the subcutaneous tissue of the back or flank, with a mass size of 3 cm or greater. A common example is excision of a subcutaneous lipoma. The surgeon opens the skin, dissects the mass from surrounding tissue, removes it, and closes the wound. General surgeons and other surgeons who treat soft-tissue masses may perform the procedure in an office or surgical facility, depending on the case and setting.

Select the code based on the mass’s location, tissue plane, and size—not the length of the incision. The operative report should identify the back or flank site, establish that the mass was subcutaneous, document its size, and describe excision rather than sampling alone. CMS assigns a 90-day global period, including the day-before preoperative visit and 90 days of related postoperative care. For multiple procedures in one session, the highest-valued procedure is paid in full and other procedures are subject to the standard 50% reduction. An assistant at surgery may be paid; co-surgeons and team surgery are not permitted. A bilateral adjustment does not apply, and modifier 50 is inappropriate.

This summary was written with AI assistance from CMS physician fee schedule data and checked against the CMS billing rules shown here. Rates on this page come directly from CMS files.

Where 21931 pays more and less

The same RVUs, adjusted for each area’s costs. Open a locality for its calculation, history and nearby areas.

109 of 109 payment localities

21931 rates by state

Office rate range in each state. Select a state to see its payment localities.

How the 21931 rate is calculated

Each of 21931’s three RVUs is multiplied by a geographic index (GPCI) for the payment locality, added up, and multiplied by the conversion factor. Drag the indexes or enter a ZIP to see what moves the rate.

Payment rules and modifiers for 21931

21931 has a 90-day global period: related visits in that window are included in the surgery payment.

What modifiers do to the payment

When to use modifier 51

21931 compared with similar codes

How to choose

21930Soft-tissue excision

Use 21930 for a subcutaneous back or flank mass under 3 cm. This code is for a mass measuring 3 cm or larger.

21932Back tumor excision

Use 21932 when the back or flank tumor is deep rather than subcutaneous and measures under 5 cm.

21933Back tumor excision

Use 21933 for a deep back or flank tumor measuring 5 cm or larger; this code describes a subcutaneous mass.

21920Soft-tissue biopsy

Use 21920 when the service is a soft-tissue biopsy of the back, not excision of the subcutaneous mass.

Codes related to 21931

Related codes aren’t interchangeable: bill the code that matches the service performed.

Where these rates come from

FeeBase calculates base physician payments from CMS work, practice-expense and malpractice RVUs, adjusted by each locality’s geographic indexes and the conversion factor. Services without a published rate are labeled, never given a made-up amount. Amounts are Medicare allowed amounts before claim adjustments: not a patient’s bill or a commercial rate.

CMS RVU26D · effective Oct 1, 2026 through the day before Jan 1, 2027

Open CMS sourceHow we calculate rates