The tax reform bill signed into law in December will result in significant changes to the federal income tax withholding and exemption process in 2018. The IRS has not yet issued definitive guidance on this topic. See the IRS statement below:
The IRS is working to develop withholding guidance to implement the tax reform bill signed into law on December 22. We anticipate issuing the initial withholding guidance in January, and employers and payroll service providers will be encouraged to implement the changes in February. The IRS emphasizes this information will be designed to work with the existing Forms W-4 that employees have already filed, and no further action by taxpayers is needed at this time.