Register for BSO at ssa.gov/bso with a Login.gov or ID.me credential and request access to the 'Report Wages to Social Security' service.
Prepare your wage file in EFW2 format (the SSA's fixed-width Electronic Filing of W-2s specification); the file begins with a Submitter Record (RA), followed by Employer Record (RE), Employee Wage Records (RW/RO), and terminator records (RT/RF).
Validate the file locally against the current tax year's EFW2 Technical Specifications PDF available at ssa.gov/employer before upload; common errors include invalid state codes and totals mismatches.
In BSO, select 'Upload Formatted Wage File', browse to your EFW2 file, and submit; BSO automatically generates the W-3 transmittal from the file totals.
Monitor submission status in BSO; the portal will display Accepted, Accepted with Errors, or Rejected; download the error detail report for any failures and correct and resubmit.
Annual wage reports for tax year 2025 must be submitted by January 31, 2026 to avoid late-filing penalties; corrections (W-2c) can be filed year-round via BSO.
Known gotchas
EFW2 format changes slightly each tax year — always download the current year's Technical Specifications from ssa.gov/employer before building or running your file generator.
BSO imposes file size limits; employers with very large workforces may need to split submissions into multiple files; check current documentation for the applicable limit.
The 50-form online entry option in BSO is a separate workflow from EFW2 upload and is not suitable for programmatic automation; for system-to-system filing at scale, use the EFW2 upload path.
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