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N837 Remark Code: Payer Added a Missing Modifier

N837 is an alert that the claim line was missing a modifier and the payer added it during processing. The line was adjudicated with the modifier the payer supplied, so check that it reflects the service and add it yourself on future claims.

Code: N837 (RARC N837)
Status: Active In use since November 1, 2020.
Code set: Remittance Advice Remark Codes (RARC)
Group codes: CO (Contractual Obligation): If a CO adjustment accompanies the alert, it reflects how the line priced with the added modifier and is a provider write-off.
Official description: Alert: Missing modifier was added.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified: September 24, 2026 against the official X12 list.

What N837 means

Most payers deny a line when a required modifier is missing (that’s N822). Some fix simple omissions themselves instead. N837 is the alert that this happened: the payer found a missing modifier, added the one it determined was appropriate, and processed the line.

The claim went through, but not quite as you billed it. The added modifier can affect pricing, and payers that auto-correct today may deny the same omission later.

What to do

Look at the adjudicated line on the remittance to see which modifier was added.
Check it against the documentation. If it correctly describes the service, post the payment normally.
If the modifier is wrong and affected payment, submit a corrected claim with the right modifier in box 24D and resubmission code 7 in box 22.
Update your charge rules so the modifier is on future claims before they’re sent. See NCCI and modifier denials for common modifier requirements.

Codes that may appear with N837

CO-45 (Charge exceeds fee schedule/maximum allowable or contracted/legislated fee arrangement.): The line priced under the fee schedule once the modifier was applied.
CO-59 (Processed based on multiple or concurrent procedure rules. (For example multiple surgery or diagnostic imaging, concurrent anesthesia.)): Multiple-procedure rules applied, which added modifiers can trigger.

N822 (Missing procedure modifier(s).): The payer denied the line for the missing modifier instead of adding it.
N823 (Incomplete/Invalid procedure modifier(s).): A modifier was present but invalid.

N837 FAQ

Do I need to resubmit the claim?

Usually not, if the payer's modifier matches the service. If it doesn't, and payment was affected, submit a corrected claim with the right modifier.

Why would a payer add a modifier instead of denying?

Some payers correct routine omissions automatically where the right modifier is clear, such as a pricing modifier implied by the provider type.

Could the added modifier change payment?

Yes. Pricing modifiers can reduce or change the allowed amount. Compare the payment with what you expected for the modifier that applies.

Important: read before using this information

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