On January 11, the IRS posted the new 2018 tax withholding rates on IRS.gov.
Employers should begin using the new tables as soon as possible, but not later than February 15, 2018). Until employers can make the switch, they can continue to use the 2017 withholding tables until they are able to implement the new 2018 tables.
The IRS will not issue new Forms W-4 in 2018, but they have designed the 2018 withholding tables so that they will work with the existing Forms W-4. Many employees should begin to see increased in their take-home pay as a result of the lower federal tax rates sometime in February.
Software vendors and payroll professionals are already working diligently to implement the new withholding tables into existing systems.