CMS-1500 Form Guide: All 33 Boxes Explained
Every professional claim maps back to these 33 boxes — on paper and in the electronic 837P alike. Here is what belongs in each one, and where claims go wrong.
The CMS-1500 (version 02/12) is the standard claim form for professional services in the United States. Even when claims travel electronically as the 837P, every data element maps back to these 33 boxes — so understanding the form is understanding the claim. Here is what belongs in each block, and the errors that bounce claims.
Section 1: Patient and insured information (Boxes 1–13)
| Box | What goes there | Watch out for |
|---|---|---|
| 1 | Coverage type (Medicare, Medicaid, TRICARE, group health, etc.) | Wrong payer type checked = wrong routing |
| 1a | Insured's ID number exactly as printed on the card | Transposed digits are a top rejection cause |
| 2 | Patient's full name (last, first, middle initial) | Must match the payer's eligibility file |
| 3 | Patient's date of birth and sex | DOB mismatches deny as "patient not identified" |
| 4 | Insured's name (if different from the patient) | Keep consistent with Box 6 relationship |
| 5 | Patient's address and phone | — |
| 6 | Patient's relationship to the insured (self, spouse, child, other) | Drives coordination of benefits |
| 7 | Insured's address and phone (if different) | — |
| 8 | Reserved (NUCC use) | Leave blank |
| 9 / 9a–9d | Other insured's name, policy and plan details (secondary coverage) | Missing secondary data breaks COB claims |
| 10 | Is the condition related to employment, an auto accident, or another accident? | "Yes" answers route claims to workers' comp / auto payers |
| 10d | Claim codes (NUCC-defined condition codes) | — |
| 11 | Insured's policy / group number | Required when another payer is primary |
| 11a–11c | Insured's DOB/sex, employer or school, insurance plan/program name | Feeds the primary-vs-secondary decision |
| 11d | Is there another health benefit plan? (Yes/No) | A wrong "No" here creates COB denials later |
| 12 | Patient's (or authorized person's) signature — authorizes release of information | "Signature on file" is standard for electronic claims |
| 13 | Insured's signature — authorizes payment of benefits to the provider | Missing = payment may go to the patient instead |
Section 2: Physician / supplier information (Boxes 14–33)
| Box | What goes there | Watch out for |
|---|---|---|
| 14 | Date of current illness, injury or pregnancy (qualifier 431 onset / 484 LMP) | Required for chiropractic, pregnancy and injury claims |
| 15 | Other date (qualifiers for similar illness, unable-to-work dates, etc.) | — |
| 16 | Dates the patient is unable to work in their current occupation | Used by disability-related payers |
| 17 / 17a / 17b | Referring, ordering or supervising provider name, qualifier ID and NPI | Missing ordering NPI denies labs, imaging and DME |
| 18 | Hospitalization dates related to the current services | Needed for services during an inpatient stay |
| 19 | Additional claim information (NUCC-defined supplemental data) | Narrative that has no other home |
| 20 | Outside lab? — and its charges | An incorrect "Yes" misstates who performed the lab |
| 21 | Diagnosis codes (ICD-10), lines A–L, with ICD indicator "0" for ICD-10 | Codes must be as specific as the documentation supports |
| 22 | Resubmission code and original reference number | Required on corrected claims — ties to the original claim number |
| 23 | Prior authorization number (or CLIA number for laboratory services) | Missing auth number = CO-197 denial |
| 24 | The service lines: dates (A), place of service (B), EMG (C), CPT/HCPCS + modifiers (D), diagnosis pointers (E), charges (F), days/units (G), EPSDT (H), ID qualifier (I), rendering provider NPI (J) | The densest box — pointer, modifier and unit errors live here |
| 25 | Federal tax ID (EIN or SSN) of the billing provider | Must match the payer's credentialing record |
| 26 | Patient's account number (your internal reference) | Echoed back on the ERA — key for posting |
| 27 | Accept assignment? (Yes/No) | Drives how Medicare pays |
| 28 | Total charge | Must equal the sum of the Box 24F lines |
| 29 | Amount paid (by the patient or primary payer, as applicable) | Critical on secondary claims |
| 30 | Reserved (NUCC use) | Leave blank |
| 31 | Signature of physician/supplier, with date and credentials | "Signature on file" for electronic claims |
| 32 / 32a | Service facility location name, address and NPI | Required when services were rendered outside the office or home |
| 33 / 33a / 33b | Billing provider name, address, phone and NPI (plus other ID as required) | Address/NPI mismatches with enrollment deny the whole claim |
Paper form vs the 837P
Almost all professional claims now travel electronically, but the 837P file carries the same data in loops and segments — Box 33's billing provider is the 2010AA loop, Box 24's lines are the 2400 loop, and so on. When an electronic claim rejects, translating the error back into "which box is wrong" is still the fastest way to find the problem. (The institutional counterpart for hospitals and facilities is the UB-04 form.)
Front-end accuracy here is what produces a clean claim. Elite Bill Care's claim submission team validates every required field before a claim leaves the door — the cheapest denial is the one that never happens. See also the most common medical billing errors.