By now employers should be using the updated income-tax withholding tables for 2018 which reflects changes made by the tax reform legislation. The marital status chosen on the W-4 will determine how much income tax will be withheld. Personal exemptions are no longer relevant.
On February 28, 2018, the Internal Revenue Service released the new version of Form W-4 as well as an updated Withholding Calculator which gives employees the information they need to fill out the new Form W-4 should changes need to be made.
The new tax law does not affect 2017 tax returns, however, we encourage all employees to review their personal tax situation to see if they need to make any changes to determine their proper withholding for 2018 to avoid any issues when they file next year.