The QBI deduction calculation does not seem correct. QBI is being reduced by deductible portion of SE tax

It is correct.   The 20% QBI deduction calculation compares the difference between 20% of the QBI (your Schedule C net income, minus any other deductions attributable to your Schedule C income, which encompasses deductions such as the solo 401K deduction, Self-Employed Health Insurance Deduction attributable to the business, and 1/2 of SE tax being deducted on your return) and 20% of your Taxable Income  (which encompasses other deductions and income amounts)  Whichever amount is lower is the QBI deduction.  

Why is TurboTax using this calculation?  Although there has been recommendations that these deductions not be considered for QBI considerations, here is what the IRS decided in their final regs.  What follows comes directly from their final regulations, which you can access through the link below.  I will be quoting from pages 43 and 44 of the regulation:  Final Regulations on Section 199A deduction (PDF) (Italics are added to show IRS official procedure on this provision) :

5. Treatment of Other Deductions

Section 199A(c)(1) provides that QBI includes the net amount of qualified items of income, gain, deduction, and loss with respect to any qualified trade or business of the taxpayer. Commenters requested additional guidance on whether certain items constitute qualified items under this provision. Several commenters suggested that deductions for self-employment tax, self-employed health insurance, and certain other retirement plan contribution deductions should not reduce QBI. One commenter reasoned that qualified retirement plan contributions should not reduce QBI because they should not be treated as being associated with a trade or business, consistent with the treatment when calculating net operating losses under section 172(d)(4)(D). The commenter also suggested that while self-employed health insurance is treated as associated with a trade or business, such expense should likewise not reduce QBI for purposes of simplification in administering the rule. Another commenter suggested that QBI should not be reduced by these expenses because they are personal adjustments. One commenter also requested guidance on whether unreimbursed partnership expenses, the interest expense to acquire partnership and S corporation interests, and state and local taxes reduce QBI.

The Treasury Department and the IRS have not adopted these recommendations because they are inconsistent with the statutory language of section 199A(c). Whether a deduction is attributable to a trade or business must be determined under the section of the Code governing the deduction. All deductions attributable to a trade or business should be taken into account for purposes of computing QBI except to the extent provided by section 199A and these regulations. Accordingly, §1.199A-3(b)(1)(vi) provides that, in general, deductions attributable to a trade or business are taken into account for purposes of computing QBI to the extent that the requirements of section 199A and §1.199A-3 are otherwise satisfied. Thus, for purposes of section 199A, deductions such as the deductible portion of the tax on self-employment income under section 164(f), the self-employed health insurance deduction under section 162(l), and the deduction for contributions to qualified retirement plans under section 404 are considered attributable to a trade or business to the extent that the individual’s gross income from the trade or business is taken into account in calculating the allowable deduction, on a proportionate basis. The Treasury Department and the IRS decline to address whether deductions for unreimbursed partnership expenses, the interest expense to acquire partnership and S corporation interests, and state and local taxes are attributable to a trade or business as such guidance is beyond the scope of these regulations.

To be sure, the new Section 199A deduction is taking some time to understand all of the nuance involved in the deduction.  However, the good news is that it is an extra deduction on our return that was not available before

This FAQ explains in more detail  (click on the View the entire answer, and then the embedded link  How is the deduction calculated? (Not for the faint of heart!):  https://ttlc.intuit.com/replies/7019998 

[Edited 2/11/2019 12:39 PST]

I received a notice from IRS saying I made an error on the QBI deduction.  TurboTax Calculated the QBI deduction differently than IRS.  IRS took my AGI on line 7, Form 1040 and deducted the standard deduction of 12,000. Then they multiplied that result by 20% and inserted that on line 9 on the 1040 form as the QBI deduction.    Turbotax came up with the QBI deduction by taking my Schedule C, line 31 profit and deducting 1/2 self employment tax from the profit.  Then that result was multiplied by 20% and inserted into line 9 on  Form 1040. 

Now I owe hundreds of dollars and interest to the IRS.  Intuit:  What do you have to say about this?  Who made the error? Please explain.

Please I need your help guys

as I am filing my taxes- I face some confusing for QBI form- I did two separate Schedules C for self-employment- and did1 schedule SE for both where I calculate the total profit of both and I got the total tax self-employment deduction- 

when it comes to filling out the QBI- I wonder how to do column c  for each business where is the qualified business income- meaning is it ok to minus each business profit from the total amount self-employed tax deduction that I have in one Sch SE? my confusion is because that tax amount is combined both businesses in one form, so should I do two schedules SE?