the max you can contribute is the lesser of $6000 or your net income from self-employment (schedule C) less 1/2 self employment tax. any excess and earnings thereon would have to be withdrawn by 4/15/2020.
self employment tax for those making less than about $128,000 is about 14.13% (.9235 times 15.3%)of net SE income . it can not be avoided by making an IRA contribution.
in addition to self employment income ,W-2 income would increase the amount you can contribute.
don't know your tax status but perhaps you would be better off making a Roth IRA contribution instead. Same limit and you would still end up owing the SE tax, but your regular income taxes could still be $0 (your standard deduction could result in no taxable income). you would also need to take into a/c state taxes if any
