Which form is used to help determine how much to withhold from an employee's wages for taxes?

The form used to help determine how much to withhold from an employee's wages for taxes is the W-4 form. The W-4, also known as the Employee's Withholding Certificate, is completed by an employee upon hiring. It provides necessary information about the employee’s filing status and the number of allowances they claim, which helps the employer calculate the appropriate federal income tax withholding from the employee’s wages.

The Payroll Register is a record that includes all employees' wages and taxes withheld for a specific pay period but does not guide the withholding process itself. Circular E is the IRS publication that contains federal tax withholding guidelines, but it doesn't serve the same function as the W-4, as it does not collect information directly from employees. Form 1099 is used to report various income received other than wages, salaries, or tips and is not related to employee withholding.

Thus, the W-4 is the crucial form for establishing how much tax an employer needs to withhold based on each employee's unique tax situation.