TurboTax is probably calculating the SE tax based on your wife's self employment income based on her 1099-NEC.
When you enter a 1099-NEC it defaults to reporting as self employed on Schedule C.
The self-employment tax (officially known as the SECA tax for Self-Employment Contributions Act tax) is the self-employed person's version of the FICA (Federal Insurance Contributions Act) tax paid by employers and employees for Social Security and Medicare, and it's due on your net earnings from self-employment.
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The Self-Employment Tax - TurboTax Tax Tips & Videos
