If self-employed you can list the Medicare paid out of pocket. TurboTax will then determine how much can be deductible on the Sch C based on the profit the Sch C has.
TurboTax will determine the amount however here is an IRS worksheet that show you the calculation.
https://taxmap.irs.gov/taxmap/instr/i1040gi-042.htm#en_us_publink10002107
