Why do I pay self-employment tax if my taxable income is $0?

[JDH]

Bus. Income line 12 = $49,217.   IRA dist. line 15b = $20,000.  AGI line 37 = $50,365.  Item Deducts line 40 = $46,897.  Exempts line 42 = $12,000.

Taxable Income line 43 = $0.

Tax Year is 2015

[JulieCo]

Your taxable income amount determines your income tax amount due.  But, for self-employment income, the self-employment taxes are still due on that income as they are not income taxes, but the taxes for FICA/MCARE that employers and employees pay on wages.  For self-employed businesses, both the employer and employee portion of the FICA/MCARE taxes are due on the self-employed income. 

See more information in this FAQ below on self-employment taxes:

https://ttlc.intuit.com/replies/3301474

Plus, see the link of this TurboTax article on Self-Employed Federal Income Taxes which touches on both the income tax and self-employment taxes.