Employers that filed 250 or more IRS Forms W-2 for the prior calendar year must include the aggregate cost of employer-sponsored health plan coverage on employees’ Forms W-2. This reporting is optional for employers that had to file fewer than 250 Forms W-2 for the prior calendar year. Employers must file Forms W-2 with the Social Security Administration and furnish Forms W-2 to employees by Jan. 31 of each year unless an extension applies.