The employee Social Security tax withholding rate is 7.65 percent as of 2015, according to the Social Security Administration. That number is matched with an employer contribution of 7.65 percent. The rate includes the Social Security portion, which is 6.20 percent, and the Medicare portion, which is 1.45 percent.
The Social Security tax rate for self-employed individuals is 15.3 percent, as noted by the SSA. The SSA publishes an official table of the rate and other information about Social Security taxes on its website, SSA.gov. This includes information for exempt retirement benefit amounts that may not be subject to regular withholding taxes.