How to bill bilateral procedures with modifier 50
Bill a bilateral procedure to Medicare on one line with modifier 50 and one unit, unless the code's own wording already says bilateral. The bilateral surgery indicator for that code in the CMS fee schedule file then decides whether the pair pays at 150 percent or at 100 percent of the single-side amount.
Written by Salman Saeed, CEO and Co-Founder · Reviewed by a Certified Medical Coder · 
In short: read the code wording first, look up its indicator second, and only then build the line. Most surgical codes with indicator 1 take 50 with one unit, an ASC reports two lines instead, and the indicator tells you what the remittance should show.
What are the steps to bill a bilateral procedure?
Follow the same five checks every time, in this order. The modifier 50 code page defines the modifier, and this post is the working sequence for the claim. The rules come from chapter 12, section 40.7 of the Medicare Claims Processing Manual, chapter 4, section 20.6.2 and the NCCI Policy Manual.
- Read the code's descriptor. If it says bilateral, or unilateral or bilateral, report one unit with no modifier 50 and no LT or RT.
- Find the code in the relative value file and read the BILAT SURG column. That is the bilateral surgery indicator: 0, 1, 2, 3 or 9.
- Build the line for your setting. A physician or outpatient hospital reports 50 with 1 unit on a single line. An ASC reports two lines, one with LT and one with RT, 1 unit each.
- If the work was at different sites on each side, report one unit with 50 for each site.
- Compare the remittance with what the indicator predicts before you post it.
What do the indicators look like on real codes?
The October 2026 file (RVU26D, released 08/26/2026) gives these values. Descriptors below are paraphrased, and the NCCI manual states what a bilateral claim looks like for each indicator.
| Code | Plain meaning | Indicator | Bilateral claim |
|---|---|---|---|
| 64721 | Carpal tunnel release at the wrist | 1 | One line, 50, 1 unit |
| 28296 | Bunion correction with a metatarsal cut | 1 | One line, 50, 1 unit |
| 29881 | Knee scope with meniscus removal | 1 | One line, 50, 1 unit |
| 27395 | Thigh tendon lengthening, wording already says bilateral | 2 | One line, 1 unit, no 50 |
| 77066 | Diagnostic mammography, wording says both breasts | 2 | One line, 1 unit, no 50 |
| 77065 | Diagnostic mammography, one breast | 0 | Do not use it twice. Report the both-breast code |
| 73560 | Knee X-ray, 1 or 2 views | 3 | Any of: 2 units on one line, 50 on one line, or RT and LT lines |
Indicator 9 means the concept does not apply, so no bilateral claim should exist for that code. When the file and the descriptor seem to disagree, trust the descriptor for the unit count and the file for the payment rule, and look for a code that describes the bilateral version.
What does a bilateral claim look like with real numbers?
Take a patient who has carpal tunnel release on both wrists in one session. The code has indicator 1, so the standard 150 percent rule applies. The dollar figures here are made up to show the arithmetic.
The Medicare amount for one wrist is $600. The practice bills $1,100 for the pair.
Chapter 12, section 40.7 C says the payment is the lower of the billed amount or 150 percent of the fee schedule amount, and the RVU file adds that the adjustment comes before any multiple procedure rule. If the same patient also had another procedure on the same day, the pair is priced first and then the multiple procedure reduction is applied.
Medicare's claim systems can recognize bilateral surgery from either 50 or the same code on two lines with LT and RT. That is a processing instruction. The NCCI manual still requires practitioners and outpatient hospitals to report 50 with one unit, and it builds MUE values on that single line.
Which settings and payers change the build?
Three exceptions come up in daily work. In each, the safe habit is to confirm the rule before the line is built.
- Hospital outpatient: chapter 4, section 20.6.2 says 50 is for operative sessions only and not to submit two line items, and not to add RT or LT when 50 applies.
- Ambulatory surgical centers: the single-line rule does not apply, so a bilateral surgical procedure goes on two lines, 1 unit each, with LT on one and RT on the other.
- Commercial payers: Chapter 12 notes that Medicare's single-line rule differs from the CPT guideline of two line items. Private plans set their own modifier policy, so read it before you assume the Medicare build.
Two surgeons operating on one side each are not a bilateral case. Chapter 12, section 40.8 treats that as co-surgery with modifier 62, which the total knee replacement code page walks through.
Which denials follow a wrong bilateral claim, and what fixes them?
| Remit shows | What went wrong | Fix |
|---|---|---|
| CO-4, procedure inconsistent with the modifier | 50 on a code whose wording is already bilateral, or LT with 50 | Remove 50 or the side modifier and send a corrected claim |
| CO-97 or CO-18 on the second line | Two lines for one bilateral surgery | Merge to one line with 50 and 1 unit |
| Pays 100 percent, not 150 | Indicator is 0, 2 or 3, so no bilateral adjustment applies | No error. Post it and update your expected-payment table |
| Pays one side only | 50 missing, so the payer saw one wrist | Add 50 with the operative note and send a corrected claim |
The NCCI edits page covers pairs, and the medically unlikely edits page covers the unit caps that a 2-unit line can trip on a surgical code. For a repeat of a procedure on the same side rather than the other side, see modifier 76 versus 77.
How Nucleus Align handles it
Our medical coding team includes AAPC and AHIMA certified coders, and we work denials within 48 hours. We keep an indicator table by code so the expected payment is known before the remit arrives, a habit that suits orthopedic billing. Book a call to review your surgical claims, or read more on the blog.
- Medicare Claims Processing Manual, chapter 12, section 40.7 · CMS
- Medicare Claims Processing Manual, chapter 4, section 20.6.2 · CMS
- NCCI Policy Manual for Medicare Services, 2026 (chapters I and III) · CMS
- Physician Fee Schedule relative value files (RVU26D) · CMS
- Claim adjustment reason codes · X12
We check every rule, code and deadline against the official source. See our editorial policy.
Common questions
Straight answers from the team that does the work.
Ask a billing lead directly. A 20-minute call, Monday to Friday, 9am to 5pm Eastern.
01How do you bill bilateral procedures with modifier 50?
Report the code once with modifier 50 and one unit when the work was done on both sides in the same operative session and the code's wording does not already say bilateral. Medicare wants a single line. Check the bilateral surgery indicator for the code to know whether the pair pays at 150 percent or 100 percent.
02What does Medicare pay for a bilateral procedure?
For indicator 1, the lower of the billed amount or 150 percent of the fee schedule amount for a single code, per chapter 12, section 40.7 C. For indicators 0, 2 and 3 the adjustment does not apply, and payment is the lower of the billed amount or 100 percent. Other pricing rules apply after the bilateral adjustment.
03Should an ASC use modifier 50?
No. The NCCI manual says the single-line rule does not apply to an ambulatory surgical center. An ASC reports a bilateral surgical procedure on two lines, each with 1 unit, one with LT and one with RT. Other payers may set their own rule, so confirm it in the payer's manual.
04Where do I find the bilateral indicator for a code?
It is in the BILAT SURG column of the CMS physician fee schedule relative value file. The file's documentation defines the values 0, 1, 2, 3 and 9. Look the code up in the release that covers the date of service.
Talk to a billing lead.
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