Per IRS Publication 334, page 9:
SE tax is a social security and Medicare tax primarily for individuals who work for themselves. It is similar to the social security and Medicare taxes withheld from the pay of most wage earners.
Caution If you earned income as a statutory employee, you do not pay SE tax on that income. Social security and Medicare tax should already have been withheld from those earnings.
Social security coverage. Social security benefits are available to self-employed persons just as they are to wage earners. Your payments of SE tax contribute to your coverage under the social security system. Social security coverage provides you with retirement benefits, disability benefits, survivor benefits, and hospital insurance (Medicare) benefits.
Caution Be sure to report all of your self-employment income. By not reporting all of it, you could cause your social security benefits to be lower when you retire.
Who must pay SE tax. You must pay SE tax and file Schedule SE (Form 1040) Self-Employment Tax if either of the following applies:
Caution The SE tax rules apply no matter how old you are and even if you are already receiving social security or Medicare benefits.
To report your self-employment income in the TaxAct® program, go to our Schedule C - Entering Sole Proprietorship in Program FAQ. After entering your self-employment income, you can view your self-employment tax:
Note that any link in the information above is updated each year automatically and will take you to the most recent version of the webpage or document at the time it is accessed.