CMS 1500 Form Fields Explained, From Box 1 to Box 33

Here are the CMS 1500 form fields explained in order. Boxes 1 to 13 identify the patient, the insured and the plan. Boxes 14 to 23 cover the condition, the referring provider, diagnosis codes and authorizations. Box 24 holds up to six service lines. Boxes 25 to 33 name the billing provider, tax ID, totals and service location.

What do CMS 1500 patient and insured boxes 1 to 13 ask for?

CMS 1500 boxes 1 to 13 ask who the patient is, who holds the insurance policy and which plan the claim goes to. The top half of the form also records other coverage, whether the condition is tied to work or an accident, and whether signatures authorizing release of information and payment are on file.

The CMS 1500, also called the 1500 Health Insurance Claim Form, is the paper claim used by physicians, other professionals and suppliers. The current version is dated 02/12. The industry guide to filling it in is the NUCC 1500 Claim Form Reference Instruction Manual, which NUCC updates each July. Medicare publishes its own instructions in the Medicare Claims Processing Manual, chapter 26. Other payers can add their own rules.

One NUCC rule shapes the whole top half. If the patient has their own member ID number, the patient is treated as the insured, and their details go in the insured fields rather than the patient fields.

Every sample value in the tables in this post comes from one fictional claim. The patient is Jordan Sample, the member ID is XJH000111222 and the practice is Example Medical Group. None of these are real.

Four fields in the top half are reserved: 8, 9b, 9c and later box 30. NUCC explains that each one used to hold data that no longer exists in the electronic claim standard, so the field was eliminated and is now reserved for NUCC use. Patient status, the other insured's birth date and the employer or school name used to sit there.

Box 1a and box 11 come from the member's insurance card. Reading the right number off a card, and telling a member ID from a group number, is covered in the guide to member ID and group number on insurance cards.

CMS 1500 physician and supplier boxes 14 to 23

CMS 1500 boxes 14 to 23 hold the clinical and administrative context for the services. They record dates tied to the illness, the provider who referred or ordered care, hospital dates, outside lab charges, the diagnosis codes in box 21, any resubmission reference and the prior authorization number.

Several of these boxes pair a date or name with a short qualifier code that says what the value is. Box 14 uses 431 for onset of current symptoms or illness and 484 for last menstrual period. Box 17 uses DN, DK or DQ to say whether the named person referred, ordered or supervised the service.

Box 21 is the anchor for the service lines. NUCC says to enter the ICD indicator (0 for ICD-10-CM), list no more than 12 codes, and leave out the decimal point because it is implied. Each service line then points back to these lines by letter in box 24E. How those letters work, including the four-letter limit and Medicare's one-letter rule, is explained in the guide to how CMS 1500 diagnosis pointer letters map to box 21.

Box 22 is only for claims that replace or cancel an earlier one. NUCC lists frequency code 7 for a replacement and 8 for a void, entered on the left with the payer's original reference number. NUCC says the box "is not intended for use for original claim submissions."

Box 23 holds one payer-assigned number. NUCC lists prior authorization, referral, mammography certification and CLIA numbers as the options. Chapter 26 adds that for Medicare, box 23 "can contain only one condition", and anything more needs a separate claim form.

Reading one CMS 1500 service line across columns 24A to 24J

A CMS 1500 service line runs across columns 24A to 24J and describes one billed service: when it happened, where, what was done, why, what it cost, how many units and who performed it. The form has six service lines, and each line is split into a shaded top half and a white bottom half.

The shaded top half is for supplemental information, not for extra lines. NUCC says it "is not intended to allow the billing of 12 lines of service." It holds items such as a National Drug Code (NDC) with qualifier N4, a narrative for an unspecified code with ZZ, or a contract rate with CTR, starting at 24A. A claim with more than six services continues on another page, and NUCC says a claim with more than 50 service lines must be split.

The sample line uses place of service 23, which chapter 26 lists as Emergency Room-Hospital, and procedure code 99283, which the Medicare Claims Processing Manual, chapter 4 shows on an emergency room line in one of its examples. The rendering NPI is the example number CMS uses in its paper on NPI check digit requirements.

Three columns trip people up:

• 24A and 24G together. NUCC allows one line to cover a series of identical services only on consecutive days, and "the number of days must correspond to the number of units in 24G."
• 24G for anesthesia. NUCC says anesthesia is reported in minutes. Chapter 26 says the same for Medicare and tells billers to convert hours to minutes.
• 24I and 24J when the rendering and billing provider are the same. NUCC says to report the rendering ID "only when different from data recorded in items 33a and 33b."

The NPI in 24J identifies the individual who rendered the service, which may differ from the billing group in 33a. The differences between those numbers, with a check-digit example, are covered in where NPI and tax ID numbers sit on the CMS 1500.

What do procedure code modifiers in CMS 1500 box 24D change?

Procedure code modifiers in CMS 1500 box 24D add detail to the procedure code without replacing it. A modifier is a two-character code written after the CPT or HCPCS code on the same claim line. It can say which component of a service is billed, how it was delivered, or that more modifiers apply.

NUCC says box 24D "accommodates the entry of up to four 2-character modifiers", printed in four separate slots to the right of the procedure code. Chapter 26 confirms that the form "has the capacity to capture up to four modifiers." The code itself goes in without a narrative description.

Medicare's manuals show what procedure code modifiers on claim lines can change:

• Which part of a service is billed. Chapter 4 lists modifier 26 as the professional component and TC as the technical component. The same procedure code with 26 bills the interpretation, and with TC it bills the equipment and staff side.
• How a service was delivered. Chapter 26 says Medicare telehealth claims with place of service 02 or 10 "must be paired with the appropriate telehealth modifier", 93 for audio-only and 95 for audio and video.
• That more modifiers apply. When a line needs more than four, chapter 26 says to enter modifier 99 in 24D and list every applicable modifier in box 19, in the form 1=(mod), where 1 is the line number.

A modifier changes how a payer reads the line, so a dropped or misplaced modifier changes the claim. On a scanned form, a modifier printed in the wrong slot can be read as part of the next column. Modifier choice is a coding decision made by the provider. This section covers where modifiers sit on the form, not which one to use.

CMS 1500 billing provider boxes 25 to 33

CMS 1500 boxes 25 to 33 identify who is billing, who signed, where the service happened and what the totals are. They hold the billing provider's tax ID, the patient's account number, the assignment choice, the total charge, any amount paid, the signature, the service facility and the billing provider's NPI.

Box 26 is easy to undervalue. NUCC notes that a payer reports this account number back on the 835 remittance, so a practice that leaves it blank loses an easy way to match the payment to the patient later. The guide to how to read an EOB shows where that number reappears.

Box 28 must equal the sum of the 24F charges. Box 33 is the provider "requesting to be paid", and NUCC says it "should always be completed". The electronic claim requires the billing address to be a street address or physical location, and NUCC recommends applying the same rule on paper.

Box 25, box 32a and box 33a are the three identifiers payers use to decide whom to pay, and each has its own rules about whose number belongs there.

CMS 1500 boxes that are optional, conditional or easy to skip by mistake

On the CMS 1500, few boxes are filled on every claim. Some are reserved and stay empty, some apply only when another box is marked, and some depend on the payer. Conditional boxes are easy to miss because the box that triggers them sits elsewhere on the form.

Always blank

Boxes 8, 9b, 9c and 30 are reserved for NUCC use. NUCC says it will publish instructions if any of them is used again. A value printed in one of these boxes can be a sign of an old form layout or a print job that has drifted out of alignment.

Conditional on another box

• Boxes 9, 9a and 9d are filled only when 11d is marked YES. NUCC says that if 11d is YES, these three must be completed.
• Box 10b state must be filled when 10b says YES for an auto accident. NUCC adds that any YES in 10a to 10c may point to other insurance that pays first, which then goes in box 11.
• Box 32 must name the supplier when box 20 says YES for purchased services.
• Box 22 is used only for a replacement or void, never on a first submission.
• Box 32a is used only when the service facility NPI differs from the billing NPI.

Payer-dependent

Medicare tells billers to leave several boxes blank that other payers may want. Chapter 26 says 17a, 22, 24H, 24I, 30 and 32b are not required or not reported for Medicare, and 24C is not required. Box 19 is also payer-driven: NUCC tells users to follow "the most current instructions from the public or private payer" for its use.

Easy to skip by mistake

• Box 24G must hold 1 for a single service. NUCC says "the numeral 1 must be entered."
• Box 21's ICD indicator is a single digit above the codes, and it is easy to leave off.
• Box 27 should be reported for all payers, not only Medicare.
• Box 17b is required by Medicare whenever a physician ordered or referred the service, even though 17a stays blank.

The red dropout ink that makes the paper form readable by scanners is explained in why are paper CMS 1500 forms printed in red dropout ink. Facilities that bill on the institutional claim use a different form with 81 locators, covered in the guide to UB-04 form locators. For choosing between the two, see CMS 1500 vs UB-04. Where the claim fits in the wider billing cycle is laid out in the post on revenue cycle steps.

Schema Care reads CMS-1500 fields, diagnosis codes and procedure codes into structured data. Each field comes with a confidence score and a link to its box, and the ones it is unsure of go to a person first. The review threshold demo shows that flow on a fictional EOB.