Bonuses are considered supplemental income, which can be taxed via a percentage method or an aggregate method for federal tax purposes. The percentage method taxes bonuses at a flat rate, normally 22% with bonuses above $1 million taxed at 37%.
The aggregate method adds your bonus to your most recent paycheck and taxes the total based on the information on your W-4. Each state and in some cases localities tax bonuses as well.
Finally, Social Security and Medicare taxes are also withheld from bonuses. To figure out how much of your bonus you will take home, you need to know whether your employer will be using the flat rate or aggregate method. Then you can use the Bonus Pay Percent calculator or Bonus Pay Aggregate calculator on PaycheckCity. For more information on your bonus, visit this article.