Are you asking about qualified business expenses? The IRS defines a qualifying business expense as both "ordinary and necessary." The TurboTax FAQ I'm linking below has valuable information to help you determine what expenses are "qualified" for your business.
What self-employed expenses can I deduct?
Additionally, you should review the info in IRS Publication 535 that explains in detail what can be deducted (and how to deduct these expenses) as a self-employed individual. I'm linking that publication below.
https://www.irs.gov/pub/irs-pdf/p535.pdf
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*** I am NOT a tax expert. I am a seasoned TurboTax user, and volunteer to provide assistance to TT users. Nothing I post is to be considered TAX ADVICE; I bear no legal liability for responses.***
