How to map a Medicare 271 eligibility response to a CWF

Stedi’s Eligibility Check APIs let you get Medicare 271 eligibility responses as JSON. But your system – or one downstream – might need to display that JSON data in Common Working File (CWF) fields. Many providers still expect a CWF-style layout.

This guide shows how to map Stedi’s JSON 271 eligibility responses to CWF fields. It also covers what the CWF was, how Medicare eligibility checks work today, and why the CWF format still persists.

What Is the Common Working File (CWF)?

The Centers for Medicare & Medicaid Services (CMS) built the CWF in the 1980s to centrally manage Medicare eligibility. It was the source of truth for who was covered, when, and under which Medicare part.

The system produced fixed-format text files – also called “CWFs” – for mainframe terminals and printed reports. Each file had a set layout, with fields like member ID, coverage type, and benefit dates. For example:

How Medicare eligibility checks work today

CMS replaced the CWF in 2019 with the HIPAA Eligibility Transaction System (HETS). HETS returns standard 271 eligibility responses, the same as commercial insurers. Medicare 271s include a lot of Medicare-specific info, including:

Medicare Part A and Part B entitlements and dates
Part C (Medicare Advantage) and Part D (Prescription Drug) plan info
Deductibles, copays, and benefit limits
Remaining Skilled Nursing Facility (SNF) days
ESRD transplant or dialysis dates
Smoking cessation visits and therapy caps
Qualified Medicare Beneficiary (QMB), secondary payers, Medicaid crossover, and other coordination of benefits information.

In Stedi’s JSON 271 eligibility responses, that data lives under benefitsInformation. Each object describes a specific coverage, limit, or service type. For example:

How to use this guide

Stedi’s JSON 271 eligibility response is easier to use in modern applications. But if your customers need the old CWF layout, you’ll need to map each field from JSON.

This guide isn’t an official spec. It’s a practical reference. Each section shows a CWF-style layout, a table of field mappings, and notes on when to use each field. For details on our JSON 271 eligibility responses, see our API documentation.

Provider information

CWF field	JSON 271 eligibility response property
Organization Name	`provider.providerOrgName`
NPI ID	`provider.npi`

Patient Demographics

The following table includes patient demographics from the SUBMITTED TO PAYER and RETURNED BY PAYER sections of the sample CWF.

CWF field	JSON 271 eligibility response property	When to use
SUBMITTED TO PAYER
First Name	`subscriber.firstName`
Last Name	`subscriber.lastName`
Member ID (MBI)	`subscriber.memberId`
D.O.B.	`subscriber.dateOfBirth`
Eligibility Date(From)	`planDateInformation.eligibility` (first date)	`planDateInformation.eligibility` can be either a single date (`YYYYMMDD`) or a date range (`YYYYMMDD-YYYYMMDD`).
Eligibility Date(To)	`planDateInformation.eligibility` (second date, if present)	`planDateInformation.eligibility` can be either a single date (`YYYYMMDD`) or a date range (`YYYYMMDD-YYYYMMDD`).
Service Types(s)	`benefitsInformation.serviceTypeCodes` `benefitsInformation.compositeMedicalProcedureIdentifier.procedureCode` `benefitsInformation.compositeMedicalProcedureIdentifier.procedureModifiers`
RETURNED TO PAYER
First Name	`subscriber.firstName`
Middle Name	`subscriber.middleName`
Last Name	`subscriber.lastName`
Suffix	`subscriber.suffix`
Member ID (MBI)	`subscriber.memberId`
D.O.B.	`subscriber.dateOfBirth`
Gender	`subscriber.gender`
Address Line 1	`subscriber.address.address1`
Address Line 2	`subscriber.address.address2`
City	`subscriber.address.city`
State	`subscriber.address.state`
Zip Code	`subscriber.address.postalCode`

Benefit Information

In the JSON 271 eligibility response, benefitsInformation objects contain most of the benefits information.

The benefitsInformation.insuranceTypeCode property indicates the type of insurance policy within a program, such as Medicare. A code of MA indicates Medicare Part A. A code of MB indicates Medicare Part B. For a complete list of insurance type codes, see Insurance Type Codes in our docs.

The benefitsInformation.serviceTypeCodes property identifies the type of healthcare services the benefits information relates to. A Service Type Code (STC) of 30 relates to general benefits information. For a complete list of STCs, see Service Type Codes in our docs.

CWF field	JSON 271 eligibility response property	When to use
Effective Date	`benefitsInformation.benefitsDateInformation.plan` (first date)	All of the following must be true: `benefitsInformation.code` = `1` (Active Coverage) `benefitsInformation.insuranceTypeCode` = `MA` (Medicare Part A) or `MB` (Medicare Part B) `benefitsInformation.benefitsDateInformation.plan` can be either a single date (`YYYYMMDD`) or a date range (`YYYYMMDD-YYYYMMDD`).
Termination Date	`benefitsInformation.benefitsDateInformation.plan` (second date, if present)	All of the following must be true: `benefitsInformation.code` = `1` (Active Coverage) `benefitsInformation.insuranceTypeCode` = `MA` (Medicare Part A) or `MB` (Medicare Part B) `benefitsInformation.benefitsDateInformation.plan` can be either a single date (`YYYYMMDD`) or a date range (`YYYYMMDD-YYYYMMDD`).
Ineligible Start	`benefitsInformation.benefitsDateInformation.plan` (first date)	All of the following must be true: `benefitsInformation.code` = `6` (Inactive) `benefitsInformation.insuranceTypeCode` = `MA` (Medicare Part A) or `MB` (Medicare Part B) `benefitsInformation.benefitsDateInformation.plan` can be either a single date (`YYYYMMDD`) or a date range (`YYYYMMDD-YYYYMMDD`).
Ineligible End	`benefitsInformation.benefitsDateInformation.plan` (second date, if present)	All of the following must be true: `benefitsInformation.code` = `6` (Inactive) `benefitsInformation.insuranceTypeCode` = `MA` (Medicare Part A) or `MB` (Medicare Part B) `benefitsInformation.benefitsDateInformation.plan` can be either a single date (`YYYYMMDD`) or a date range (`YYYYMMDD-YYYYMMDD`).
Date of Death	`planDateInformation.dateOfDeath`
Lifetime Psychiatric Days	`benefitsInformation.benefitQuantity`	All of the following must be true: `benefitsInformation.code` = `K` (Reserve) `benefitsInformation.serviceTypeCodes` = `A7` (Psychiatric - Inpatient) `benefitsInformation.timeQualifierCode` = `32` (Lifetime) `benefitsInformation.quantityQualifierCode` = `DY` (Days)
Lifetime Reserve Days	`benefitsInformation.benefitQuantity`	All of the following must be true: `benefitsInformation.code` = `K` (Reserve) `benefitsInformation.serviceTypeCodes` = `30` (Health Benefit Plan Coverage) `benefitsInformation.insuranceTypeCode` = `MA` (Medicare Part A) `benefitsInformation.timeQualifierCode` = `32` (Lifetime) `benefitsInformation.quantityQualifierCode` = `DY` (Days)
Smoking Cessation Days	`benefitsInformation.benefitQuantity`	All of the following must be true: `benefitsInformation.code` = `F` (Limitations) `benefitsInformation.serviceTypeCodes` = `67` (Smoking Cessation) `benefitsInformation.insuranceTypeCode` = `MB` (Medicare Part B) `benefitsInformation.timeQualifierCode` = `22` (Service Year) `benefitsInformation.quantityQualifierCode` = `VS` (Visits) `benefitsInformation.benefitsServiceDelivery.timePeriodQualifierCode` = `29` (Remaining)
Initial Cessation Date	`benefitsInformation.benefitsDateInformation.plan`	This information is only available if an initial counseling visit was used in the past 12 months. All of the following must be true: `benefitsInformation.code` = `F` (Limitations) `benefitsInformation.serviceTypeCodes` = `67` (Smoking Cessation) `benefitsInformation.insuranceTypeCode` = `MB` (Medicare Part B) `benefitsInformation.timeQualifierCode` = `22` (Service Year) `benefitsInformation.quantityQualifierCode` = `VS` (Visits) `benefitsInformation.benefitsServiceDelivery.timePeriodQualifierCode` = `29` (Remaining)
ESRD Dialysis Date	`benefitsInformation.benefitsDateInformation.discharge`	All of the following must be true: `benefitsInformation.code` = `D` (Benefit Description) benefitsInformation.serviceTypeCodes = `RN` (Renal)
ESRD Transplant Date	`benefitsInformation.benefitsDateInformation.service`	All of the following must be true: `benefitsInformation.code` = `D` (Benefit Description) `benefitsInformation.serviceTypeCodes` = `RN` (Renal)
ESRD Coverage Period	`benefitsInformation.benefitsDateInformation.plan`	All of the following must be true: `benefitsInformation.code` = `D` (Benefit Description) `benefitsInformation.serviceTypeCodes` = `RN` (Renal)