The IRS has completed updating its online withholding calculator that individual taxpayers can use to determine how many withholding allowances they should claim for 2018. The IRS also issued a new 2018 Form W-4, Employee’s Withholding Allowance Certificate. The IRS had previously announced that taxpayers could use the old 2017 Form W-4, as modified in Notice 2018-14, until 30 days after the new form was issued.