Under current law, employees annually pay 6.2 percent of their salary or wages, up to $94,200, in Social Security taxes.  This translates into $5,840.40 a year if an employee make at least this much.

Employees also pay 1.45 percent in Medicare taxes on their entire salary or wages every year.

Thus, at least 7.65 percent of an employee's first $94,200 in salary or wages is paid to the federal government.  State and local employment taxes are then tacked on to this amount. 

Employers have to match these contributions, which really means the cost is either passed on to employees in the form of lower wages, or to customers in the form of higher prices.

Source:  www.socialsecurity.gov.