TurboTax automatically calculates your Qualified Business Income (QBI) deduction based on the entries you make for QBI businesses (Schedule C self-employment income, Schedule E rental income) or the entries you make for QBI income "passed through" from other businesses (1099-DIV, Schedule K-1). There are limits on the calculation, however, and losses from 2018 for a QBI business will offset income in 2019 before the QBI deduction is calculated.
If you provide the details on the source of your QBI, it will help diagnose your issue.
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