Meaning of box d

[macuser_22]

Box "d" on a W-2 is the optional control number that some employers use, others do not.   It is sometimes used by payroll companies that make W-2's available for import as a "password" to be able to import the W-2, other companies use other methods to verify that you actually have the W-2 and are not trying to import another persons W-2.

[SweetieJean]

On a W-2? That is an internal number that is not required for tax filing.