What is Form W-2?
The W-2 is the wage statement your employer sends you and the IRS each January. It's the master record of what you were paid and what was withheld.
How it works
Every box maps to a line on your return: Box 1 is your taxable wages, Box 2 is federal tax withheld, and Boxes 3–6 cover Social Security and Medicare. You (or your software) copy these figures straight onto Form 1040. Because the IRS gets a copy too, the numbers have to match.
A quick example
What people get wrong
Employers must furnish W-2s by January 31. If yours is missing or wrong by mid-February, contact payroll first — filing with an estimated or incorrect W-2 is a common cause of IRS notices.