Withholding is a process where employers withhold a portion of employees' wages in order to pay for their income tax, Social Security, and Medicare taxes. Withholding is an essential part of a paycheck, and is done in order to save employees from making a lump sum payment of taxes at the end of the year.

Employers calculate the withholding of taxes based on the total wages earned, and the information provided in a Form W-4 by the employee upon hire. Form W-4 requires the employees to enter details such as marital status, as well as the number of dependents they may have such as children or elderly parents, so that the employer can accurately calculate the withholding rate. This way, employees are opting to pay or receive larger amounts of taxes depending on their individual income situation.

Along with income tax withholding, Social Security and Medicare taxes are also withheld from employees wages. Employers are responsible for collecting and preparing the payments for Social Security and Medicare taxes. The percentage of wages withheld for these two taxes is generally similar, and can only change if the employee is earning a large amount of income. Employees, however, cannot opt-out of paying Social Security and Medicare taxes, as these payments are mandatory for all employees.

State withholding rates for state income tax also vary from one state to another. Employers' state withholding rates will vary depending on the state and should be adjusted for the employees' individual tax situation.

Overall, withholding can be beneficial to employees as it decreases their taxable income and allows them to pay taxes throughout the year in a more manageable way. It is, however, important to note that withholding is an estimate and employees may owe or receive money at the end of the year depending on their individual income situation. Accurately completing a Form W-4 as well as adjusting the state withholding rate can help ensure that employees do not end up owing taxes when tax season arrives.