The IRS recommends for employees to consider completing a new W4 (Form W-4) each year and when personal or financial situation change. In general, employees should complete a new W-4 any time they have a life change that impacts tax liability and thus the information on their W-4. For example, if an employee get married, they can change their filing status. If they have a baby, they can update withholding allowances. If they claim exempt during any tax year, they must update the Form W-4 by February 15 of the next year.
For answers to the most common W-4 questions, visit this PaycheckCity article.