IRS issued a statement December 26, 2018, saying that it was working to develop withholding guidance to implement the new tax law. IRS said that it expected initial withholding guidance to be issued in January, with employers and payroll service providers encouraged to implement the changes in February. The guidance will be created to work with the existing Forms W-4s, and no further action should be needed by the taxpayers.
The new 2018 withholding guidelines should allow taxpayers to see changes in their paychecks as early as February. In the meantime, IRS directed that employers and payroll service providers should continue to use the existing 2017 withholding tables and systems.