Why is payroll not withholding federal taxes on an W-4 employee with 3 dependents?

Let me share some information, @arnoldandson.

In QuickBooks Online, taxes are calculated based on the Number of allowances/dependents, taxable wages, filing status, or pay frequency. 

If a paycheck shows $0.00 or no income tax withheld, it may be caused by any of the following:

• They are not meeting the taxable wage base.
• They were set to Do Not Withhold for federal and state income taxes in the employee setup.

To check if an employee was set to Do Not Withhold, you may refer to this article: 0.00 or no income tax withheld from the paycheck.

 I also recommend checking out these articles for more information:

• Federal and state income tax.
• Payroll tax wage bases and limits.

Please leave a comment below if you have any other questions or concerns. I'll be more than happy to help. Have a good one!