UPDATE: The IRS has pushed the Form W-4 changes to 2020.
The IRS stated, ''Following feedback from the payroll and tax communities, the Treasury Department and the IRS will incorporate important changes into a new version of the Form W-4, Employee’s Withholding Allowance Certificate, for 2020. The 2019 version of the Form W-4 will be similar to the current 2018 version. A new draft version of the W-4 for 2019 will be available in the coming weeks."
The proposed 2019 Form W-4 reflects major changes including the elimination of the number of allowances, and the new marital status box – Head of Household.
At this time, all current employees’ W-4 forms are still valid. However, all new employees hired after December 31, 2018, and all employees filing exempt in 2018, will need to use the new 2019 Form W-4 form beginning January 1, 2019.
The IRS is strongly encouraging, but not mandating, all employees to file a new Form W-4 for 2019.
Employees may use the IRS Withholding Calculator to help them complete the new 2019 Form W-4. https://www.irs.gov/individuals/irs-withholding-calculator
For a copy of the proposed instructions, go to https://www.irs.gov/pub/irs-dft/iw4--dft.pdf
For a copy of the proposed form, go to https://www.irs.gov/pub/irs-dft/fw4--dft.pdf
The estimated timeline for the release of the final version of the 2019 Form W-4 is November 2018.