The QBI deduction calculation has several different parts among its three threshold taxable income levels. At the lowest level (under the threshold of personal taxable income of $157,000 single and $315,000 joint), the QBI is calculated as EITHER 20% of your qualified business income (which is self employed business profit less self employment taxes, self employed health insurance and/or self employed retirement, etc) OR 20% of your personal taxable income less capital gains/dividends.
In TurboTax Home & Business, you can switch to FORMS mode to see the Qualified Business Income worksheets that should specify how the deduction was calculated. Below is a link for how to switch to FORMS mode:
https://ttlc.intuit.com/replies/3339204
And here is more information on the QBI deduction, including an example of how it is calculated at the different threshold levels:
https://ttlc.intuit.com/replies/7019998
