The IRS has just released the 2013 version of the IRS Publication 15, Circular E, Employer's Tax Guide.
Social Security tax rate: The year the employee Social Security tax rate has increased from 4.2% to 6.2%. The maximum wage limit is $113,700.
Medicare tax withholding: Employers must withhold an additional 0.9% Medicare tax from wages paid to an employee in excess of $200,000. This additional Medicare tax is imposed only on the employee.