The qualified business income (QBI) deduction, claimed using Form 8995 or Form 8995-A, does not directly affect the calculation of self-employment (SE) tax. The QBI deduction is an adjustment to income that reduces taxable income after SE tax has been computed. Self-employment tax is calculated based on net earnings from self-employment, which are determined before applying the QBI deduction.
However, the QBI deduction can indirectly affect the amount of self-employment tax you owe because it reduces your overall taxable income. Since SE tax is based on net earnings from self-employment (which are used to compute the SE tax before any adjustments), the QBI deduction does not reduce the SE tax base. Instead, it reduces your income after SE tax has been calculated.
Importantly, certain items that are included in QBI—such as the deductible portion of self-employment tax and self-employment health insurance deductions—are already factored into the net earnings calculation for SE tax purposes. Therefore, while the QBI deduction reduces your taxable income, it does not alter the amount of SE tax you owe, which is based on net earnings from self-employment as defined in IRS Publication 560 and Schedule SE (Form 1040).
Source:
Form 8995
Form 8995-A
Disclaimer: Always verify with current Federal or State Department of Revenue Forms and Instructions for the most accurate and up-to-date guidance.