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CO-207 Denial Code: NPI Invalid Format

CO-207 means a National Provider Identifier on the claim has an invalid format. A valid NPI is exactly 10 digits and must pass a check-digit calculation. A typo, transposed digits, or a non-NPI number in an NPI field will trigger this code.

Code: CO-207 (CARC 207)
Status: Active In use since July 9, 2007; last modified June 1, 2008.
Code set: Claim Adjustment Reason Codes (CARC)
Group codes: CO (Contractual Obligation): The provider is responsible for the data error. The amount isn't billable to the patient.
Official description: National Provider identifier - Invalid format
X12 Claim Adjustment Reason Codes, retrieved September 25, 2026
Last verified: September 24, 2026 against the official X12 list.

What CO-207 means

CARC 207 reads “National Provider identifier - Invalid format.” Every NPI has a fixed structure: 10 numeric digits, with the final digit a check digit computed from the first nine using the Luhn formula (with a standard prefix applied). Payers and clearinghouses validate this automatically. If a number in an NPI field doesn’t fit, the claim is denied or rejected.

Because format validation is automatic, CO-207 almost always means a data entry or mapping problem, not a question about the provider’s status.

Example: a biller keys a referring NPI from a handwritten referral and swaps two digits. The resulting number fails the check digit, and the payer denies the claim CO-207 with remark N286.

Common causes

Typos or transposed digits in manually entered NPIs.
Too many or too few digits, often from copying with spaces or dashes.
Legacy or payer-specific IDs (such as old PINs or Medicaid numbers) entered in NPI fields.
Tax IDs entered in an NPI field.
Clearinghouse or software mapping that truncates or pads the number.
Placeholder values left in templates, such as all zeros or a test number.
Numbers read from faxed or handwritten referrals, where similar-looking digits are easy to confuse.

How to fix it

Find the invalid NPI using the remark code or by checking boxes 17b, 24J, 32a, and 33a.
Verify the correct NPI in the NPPES registry.
Submit a corrected claim (resubmission code 7 in box 22) or a new claim if the original was rejected as unprocessable.
Fix the source: the provider profile, referral directory, or template that supplied the bad number.

How to prevent it

Validate NPIs with a check-digit test at data entry.
Maintain a verified directory of referring and ordering providers.
Keep legacy and payer IDs in their own secondary identifier fields, never in NPI fields.
Scrub claims before submission. The Claims Validator catches malformed identifiers. For more on identifier issues, see NPI and enrollment denials.

Remark codes that may appear with CO-207

N290 (Missing/incomplete/invalid rendering provider primary identifier.): The rendering provider NPI is invalid.
N286 (Missing/incomplete/invalid referring provider primary identifier.): The referring provider NPI is invalid.
N433 (Resubmit this claim using only your National Provider Identifier (NPI).): Resubmit the claim using only your NPI, not a legacy identifier.

CO-206 (National Provider Identifier - missing.): The NPI was missing entirely.
CO-16 (Claim/service lacks information or has submission/billing error(s).): A general missing or invalid data denial.
CO-185 (The rendering provider is not eligible to perform the service billed.): The NPI is valid but the rendering provider isn't eligible.

CO-207 FAQ

How can an NPI fail format checks?

NPIs are 10 digits, and the last digit is a check digit calculated with the Luhn algorithm. A single mistyped digit usually makes the check digit fail, which payers and clearinghouses catch automatically.

What's the difference between CO-207 and CO-206?

CO-206 means the NPI was missing. CO-207 means something was entered, but it isn't a validly formatted NPI.

Can a valid-format NPI still be wrong?

Yes. An NPI can pass format checks but belong to another provider. That typically produces different denials, such as eligibility or enrollment codes, rather than CO-207.

Can I check an NPI's format myself?

Yes. Look the number up in the NPPES registry. If it isn't found, it's either mistyped or not an NPI. Many billing systems also run the check-digit test at entry.

Should I appeal CO-207?

No. Formatting errors are fixed by resubmitting with the correct NPI. An appeal won't change a malformed identifier.

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