What determines the percentage of gross pay which will be withheld for taxes?

The percentage of gross pay withheld for taxes is determined by several factors, including the employee's income level, filing status (single, married, etc.), and the number of allowances claimed on their W-4 form. Additionally, federal, state, and local tax rates, as well as any applicable deductions or credits, influence the withholding amount. Employers use IRS tax tables and state guidelines to calculate the appropriate withholding for each paycheck. Changes in tax laws or personal circumstances can also affect the withholding percentage.