What is Self-Employment Tax, and is this in addition to the regular taxes I will typically pay at the end of the year?

Self-employment tax is its own tax. It is a tax you will need to pay on top of any other taxes you may owe. It is the self-employed individual’s very own version of FICA tax, which is typically paid by employers and employees for Social Security and Medicare. It is due on your net earnings from self-employment.
Many newly self-employed people – sole proprietors, independent contractors…etc, are surprised at their tax bills at the end of the year because they notice they’re paying a lot more in taxes. This is because they are required to pay both the employer and employee portion of Social Security and Medicare, which is 15.3% total.