The current Social Security tax rate is 6.2% for both employers and employees, and the 2017 maximum earnings amount subject to Social Security tax is $127,200. This translates to a maximum Social Security tax of $7,886.40 for an individual.
Self-employed individuals are responsible for paying both the employer and employee portion of the Social Security tax, or a rate of 12.4% altogether, up to the maximum taxable amount. In other words, the highest Social Security tax a self-employed individual would have to pay in 2017 would be twice that of an individual employee, or $15,772.80. Technically, this is the maximum Social Security tax that could be assessed to any single person for the 2017 tax year.