What is the number for box 18 on the 1040, under "Wages, Tips, Etc."? How do I calculate this number and what is included?

I am not sure what form you are asking about. Line 18 of Form 1040 does not correspond to your question.

If you are asking about Box 18 of your Form W-2 Box 18 reports the total amount of wages subject to local income taxes. You may also have multiple local W-2 forms if you worked in more than one locality during the year. Many times, this will be the same number as the earnings listed in boxes 1 and 16. This will be blank if an employee does not pay any local taxes.

If you believe your W-2 was issued incorrectly, you should contact your employer/payroll company to discuss and have a corrected form issued if necessary. In general, you should enter your Form W-2 into TurboTax as it is shown.

The instructions for Form W-2 Box 18 say the following: Boxes 15 through 20—State and local income tax information (not applicable to Forms W-2AS, W-2CM, W-2GU, or W-2VI).  Use these boxes to report state and local income tax information. Enter the two-letter abbreviation for the name of the state. The employer's state ID numbers are assigned by the individual states. The state and local information boxes can be used to report wages and taxes for two states and two localities. Keep each state's and locality's information separated by the broken line. 

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