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CMS-1500 App

Independent resource. Not affiliated with CMS, the NUCC, the AMA, or any payer. Claim data stays in your browser.

Why CMS-1500 claims get rejected

Most “rejections” are formatting or completeness problems that never reach medical review. Here is how to tell them apart — and how to fix the form.

Last reviewed against the NUCC 1500 Reference Instruction Manual (v13.0 7/25) and CMS Pub 100-04 Ch. 26 on .

Rejection, returned as unprocessable, or denied?

Front-end EDI rejection fails clearinghouse or payer intake (often on a 277CA). It never reaches adjudication — fix and resubmit as a new claim.

Returned as unprocessable (RTP) reaches the Medicare Administrative Contractor but is not adjudicated. It often comes back as CO-16 + MA130 plus a remark code. Per CMS Pub 100-04 Chapter 1 §80.3, RTP is not appealable — correct and resubmit; do not file an appeal.

Denied means the claim was adjudicated and refused on coverage or clinical grounds. That one is appealable.

About the list below

The order below follows CGS Administrators (Jurisdiction 15) published Part B counts for Kentucky and Ohio only. No Medicare contractor publishes a national ranked list of RTP reasons as percentages — sources publish counts, not rates. We do not invent percentages.

Several top causes cannot be checked from the form alone (CPT validity on the date of service, PECOS enrollment, coverage). The checker is honest about those limits.

Common unprocessable / rejection causes (form-relevant)

  • Procedure code invalid on date of service (e.g. M20)

    Box
    24D
    What to do
    Confirm the code was effective on the date of service. Requires licensed code data we do not ship.
    Checker?
    Format only

  • Missing/invalid ordering or referring provider NPI (N285/N286)

    Box
    17 / 17b
    What to do
    Enter qualifier DN/DK/DQ and a valid 10-digit NPI. PECOS enrollment needs a registry — not checked here.
    Checker?
    Partial

  • Missing/invalid MBI (N382)

    Box
    1a
    What to do
    Enter the 11-character MBI; letters S,L,O,I,B,Z are never used.
    Checker?
    Yes (Medicare profile)

  • Missing/invalid group / billing provider (MA112)

    Box
    33 / 33a
    What to do
    Complete billing name, address, 9-digit ZIP, and NPI.
    Checker?
    Yes

  • Missing/invalid rendering provider NPI (M79, N290)

    Box
    24J
    What to do
    NPI in unshaded 24J when different from 33a; valid check digit.
    Checker?
    Yes

  • Missing primary payer info / MSP (N480, MA92…)

    Box
    11, 11c, 4, 6, 7
    What to do
    Complete insured and plan fields; Medicare may require NONE in box 11.
    Checker?
    Partial

  • Invalid procedure/modifier combination

    Box
    24D
    What to do
    Requires licensed code edits — not checked here.
    Checker?
    No

  • Diagnosis missing / not specific / external cause first (M76, MA63)

    Box
    21
    What to do
    ICD indicator 0, no decimals, greatest specificity, external-cause codes not first.
    Checker?
    Yes

  • Missing service facility name/address/9-digit ZIP (MA114)

    Box
    32 / 32a
    What to do
    Complete facility block with ZIP+4, no hyphen.
    Checker?
    Yes

  • Patient DOB format (often CO-16 + N329)

    Box
    3 / 11a
    What to do
    Use 8-digit MMDDYYYY only.
    Checker?
    Yes

Ranking context: CGS J15 (KY/OH) Part B RTP themes, not a national rate table. Always confirm against your MAC or payer remittance.

Resubmitting after a return

On the CMS-1500, box 22 carries the resubmission code and original reference number: 7 for replacement of a prior claim, 8 for void/cancel. Both parts are used together; the field is not for original submissions.

Medicare instructions say leave box 22 blank — follow your MAC’s published guidance for corrected claims on Medicare.

Before you resubmit, run the checker so the same formatting defect does not bounce the claim again.

What “clean” still does not mean

A form that passes every check on this site can still be denied for coverage, eligibility, medical necessity, or payer-specific edits. See the fixed notice on the checker page: we tell you what we can check, not whether you will get paid.

Sources

  1. Medicare Claims Processing Manual, Chapter 1 §80.3 (returned as unprocessable) (opens in a new tab) — Centers for Medicare & Medicaid Services
  2. Medicare Claims Processing Manual, Chapter 26 (Pub 100-04) (opens in a new tab) — Centers for Medicare & Medicaid Services
  3. NUCC 1500 Health Insurance Claim Form Reference Instruction Manual, Version 13.0 7/25 (opens in a new tab) — National Uniform Claim Committee
  4. CPT licensing FAQs (opens in a new tab) — American Medical Association

Last reviewed against the NUCC 1500 Reference Instruction Manual (v13.0 7/25) and CMS Pub 100-04 Ch. 26 on .

cms1500.app is an independent resource operated by AdvancedCare USA Inc. It is not affiliated with, endorsed by, or connected to the Centers for Medicare & Medicaid Services, the National Uniform Claim Committee, the American Medical Association, or any insurance payer. The CMS-1500 form is maintained by the NUCC.

Why CMS-1500 Claims Get Rejected — And How to Fix