How to map a Medicare 271 eligibility response to a CWF
Jun 2, 2025
Healthcare
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:
{..."subscriber":{"memberId":"123456789","firstName":"JANE","lastName":"DOE",...},..."benefitsInformation":[{"code":"B","name":"Co-Payment","serviceTypeCodes":["30"],"serviceTypes":["Health Benefit Plan Coverage"],"insuranceTypeCode":"MA","insuranceType":"Medicare Part A","timeQualifierCode":"7","timeQualifier":"Day","benefitAmount":"408","inPlanNetworkIndicatorCode":"W","inPlanNetworkIndicator":"Not Applicable","benefitsDateInformation":{"admission":"20241231","admissions":[{"startDate":"20240101","endDate":"20241231"}]},"benefitsServiceDelivery":[{"unitForMeasurementCode":"Days","timePeriodQualifierCode":"30","timePeriodQualifier":"Exceeded","numOfPeriods":"60","unitForMeasurementQualifierCode":"DA","unitForMeasurementQualifier":"Days"},{"unitForMeasurementCode":"Days","timePeriodQualifierCode":"31","timePeriodQualifier":"Not Exceeded","numOfPeriods":"90","unitForMeasurementQualifierCode":"DA","unitForMeasurementQualifier":"Days"},{"timePeriodQualifierCode":"26","timePeriodQualifier":"Episode","numOfPeriods":"1"}]}]}
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).
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.
For a Type of Base, use benefitsInformation.BenefitsServiceDelivery.numOfPeriods when benefitsInformation.BenefitsServiceDelivery.timePeriodQualifierCode = 31 (Not Exceeded).
For a Type of Base, use benefitsInformation.BenefitsServiceDelivery.numOfPeriods when benefitsInformation.BenefitsServiceDelivery.timePeriodQualifierCode = 29 (Remaining).
Hospital Days Colns
For a Type of Base, use benefitsInformation.BenefitsServiceDelivery.numOfPeriods when:
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Stedi is a registered trademark of Stedi, Inc. All names, logos, and brands of third parties listed on our site are trademarks of their respective owners (including “X12”, which is a trademark of X12 Incorporated). Stedi, Inc. and its products and services are not endorsed by, sponsored by, or affiliated with these third parties. Our use of these names, logos, and brands is for identification purposes only, and does not imply any such endorsement, sponsorship, or affiliation.
Stedi is a registered trademark of Stedi, Inc. All names, logos, and brands of third parties listed on our site are trademarks of their respective owners (including “X12”, which is a trademark of X12 Incorporated). Stedi, Inc. and its products and services are not endorsed by, sponsored by, or affiliated with these third parties. Our use of these names, logos, and brands is for identification purposes only, and does not imply any such endorsement, sponsorship, or affiliation.
