The Internal Revenue Service has released updates to the income tax withholding tables for 2018 which reflect the changes made by the recent tax reform. Their goal was to design the new withholding tables to work with the Form W-4’s that employees have already filed with their employers. The new payroll withholding tables can be found here: https://www.irs.gov/pub/irs-pdf/n1036.pdf
Employers should implement the 2018 withholding tables as soon as possible, but not later than February 15, 2018. Once implemented, employees will start to see changes in their withholdings.
The IRS is also working on revising the Form W-4 to reflect other changes such as the available itemized deductions, increases in the child tax credit & the new dependent credit and repeal of dependent exemptions.