Pre-tax insurance is the most common reason for your last pay stub’s year-to-date earnings to be different from your W-2 wages. If your company offers pre-tax insurance and you have participated, then the taxable wages in boxes 1, 3, and 5 will be lower by the amount of your year-to-date pre-tax insurance deductions on your last Pay Stub.

A 401(k) or SIMPLE deferral will also lower your wages in box 1 compared to your last pay stub.