What is a withholding allowance?
Employers are required to withhold money from their employees and pay Social Security, Medicare, and income taxes to the federal government. Employees don’t have anything to do with the amount of Social Security or Medicare taxes withheld, but they do have some control over how much of their paycheck is used to pay federal income taxes.
The amount that’s withheld by the employer during a calendar year often doesn’t become an issue until the next year. If too much is withheld, the employee can be owed a big refund from the government, which has basically benefitted from a loan. If too little money is withheld, the employee can be stuck with a big tax bill.