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Build SSA W-2 EFW2 File (Publication 42-007)

Skill: Convert payroll data into an EFW2 fixed-width file for SSA filing

Region: United States Category: Payroll Does: Takes annual payroll data and assembles the EFW2 fixed-width file that employers upload to the SSA Business Services Online (BSO) portal to electronically file Form W-2 Copy A. Spec: SSA Publication 42-007 (EFW2)

Every EFW2 record is exactly 512 characters, fixed-position ASCII, no delimiters. Field byte-positions and the set of required fields change by tax year — always verify the layout against the current Publication 42-007 before generating. The tables below give record purpose and the key fields, not every byte offset.

When e-filing is required

Record sequence

RA  Submitter Record                 (once, first)
RE  Employer Record                  (one per employer)
  RW  Employee Record                (one per employee)
  RO  Employee Optional Record       (optional, follows its RW)
  RS  State Record                   (optional, per state per employee)
RT  Total Record                     (totals for the preceding RE's RW records)
RU  Total Optional Record            (optional, totals of RO records)
... repeat RE...RT per employer ...
RF  Final Record                     (once, last)

RE opens an employer block; RT closes it with control totals; RF ends the file.

Key fields by record

RA — Submitter

Field Notes
Submitter EIN 9 digits
User Identifier (BSO User ID) the submitter's SSA-issued ID
Software/vendor code, company name, address contact + transmission metadata
Contact name, phone, email

RE — Employer

Field Notes
Tax year 4 digits (e.g. 2025)
Employer EIN 9 digits
Employer name, address
Kind of Employer / Employment Code e.g. Regular (941), Household, Agricultural

RW — Employee (the core W-2)

Field W-2 box
Employee SSN (a)
Employee name (first, middle, last), address (e)/(f)
Wages, tips, other compensation Box 1
Federal income tax withheld Box 2
Social Security wages / Social Security tax withheld Box 3 / Box 4
Medicare wages and tips / Medicare tax withheld Box 5 / Box 6
Social Security tips Box 7
Dependent care benefits, deferred comp (401k etc.) Box 10, Box 12 codes

RS — State (optional but usually required for state filing)

Field Notes
State code (numeric FIPS)
Employer state ID number
State wages, state income tax withheld Boxes 16 / 17
Local wages / local tax / locality name Boxes 18–20

RT — Total (per employer block)

Sum of the RW fields: total Box 1 wages, total federal tax withheld, total SS wages, total SS tax, total Medicare wages, total Medicare tax, etc., plus the count of RW records.

RF — Final

Total number of RW records in the entire file.

Data rules

Worked example (field breakdown, then assembled fixed-width)

For one employer, one employee earning $60,000 (Box 1), $6,000 federal withheld, full SS/Medicare:

RE  TaxYear=2025  EmployerEIN=123456789  Name=ACME LLC  ...
RW  SSN=123456789  Name=JANE DOE  Box1=6000000  Box2=600000
                   SSWages=6000000  SSTax=372000  MedWages=6000000  MedTax=87000
RT  NumberOfRW=1  TotalBox1=6000000  TotalBox2=600000
                   TotalSSWages=6000000  TotalSSTax=372000
                   TotalMedWages=6000000  TotalMedTax=87000
RF  NumberOfRW=1

(Box 1 $60,000 = 6000000 cents; SS tax 6.2% = $3,720 = 372000; Medicare 1.45% = $870 = 87000.) Each line is then written as a 512-character fixed-position record per Publication 42-007.

Validation checklist

Last updated: 2026-05-26 — verify exact field byte-positions, required fields, money-field formatting, and the record set against the current SSA Publication 42-007 (EFW2) for the tax year before use.