The law requires employers to withhold taxes from employee earnings to fund the Social Security and Medicare programs. These are called Federal Insurance Contributions Act taxes. Your employer also pays a tax equal to the amount withheld from employee earnings.
The self-employed pay Self-Employed Contributions Act (SECA) taxes on net earnings. SECA taxes also fund Social Security and Medicare. The self-employed pay both the employee and the employer share of SECA. But the law permits them to deduct half of the self-employment tax as a business expense.