Box 18 (W-2) may often differ from Box 1 and Box 16. The fact that it is less for you would mean your local taxes could be less than if they were the same.
Box 16: State wages.
Box 16 reports the total amount
of taxable wages earned in that state. If you worked for the same
employer in multiple state, there may be multiple lines of information.
Box 17: State income tax withheld. Box 17
reports the total amount of state income taxes withheld from your
paychecks for the wages reported in Box 16. This amount may be
deductible as part of the deduction for state and local income taxes on
Schedule A.
Box 18: Local wages.
Box 18 reports the total amount of wages subject to local, city, or other state income taxes. Often different than Box 16 and Box 1 (Federal Wages).
