Federal Withholding Tax
The IRS releases a new tax guide for each calendar year, also known as Publication 15. The tax guide contains tax tables for federal withholding tax, as well as other information. The tax tables begin on page 51 for biweekly pay. You will use the tax table that matches your W-4 marital status and allowances for biweekly pay.
The IRS has released the below income tax withholding tables for 2018 which reflects changes made by the tax reform legislation enacted.