New IRS Tools for 2018 Tax Withholding: As of Feb. 15, 2018, employers must use new tables to determine how much income tax to withhold from their employees’ paychecks. The IRS issued the required new tables in Notice 1036 on Jan. 9, 2018. The new tables are also available in IRS Publication 15. On Feb. 28, 2018, the IRS also released a revised Form W-4 and a new withholding calculator to reflect the changes. The updated tools aim to help employers improve the accuracy of their tax withholdings under changes made by the tax reform law, the Tax Cuts and Jobs Act, which was enacted on Dec. 22, 2017.