You've provided a lot of semi relevant information but in fairness to the original question, you haven't answered it.  The question started with 'I know it's income taxable' and everything you've provided has re-answered that question.   One might infer a few things from what you've provided, but they could have inferred before they started, they wanted a specific cite REGARDING SELF EMPLOYMENT SPECIFICALLY which you have not provided.  This is part of the intuit community's ongoing plague of 'here's not quite an answer,  vote for it as best answer - answer provided by top poster' and I'm sure it's not only helpful and interesting for you, but you're also putting a lot of hard work into it which should be appreciated.   But the specific question has not been answered with a relevant cite, and it might be time to say 'I couldn't find anything that's right on point'.   I think the counterpoint raised above, that unemployment replaces fica taxable income but is not fica taxable because it wasn't active, is very relevant and undermines your answers in the absence of a context link between them.