Only deductions attributable to business income should be used to reduce QBI. In the case of Schedule C, health insurance is allowable only to the extent of Schedule C business income, so it's attributable to business income and used to reduce QBI. However, in the case of a SCorp income on a K1, the health insurance deduction is attributable to the shareholder WAGES from that activity, not its business income. (The wages should already include the health insurance if the W2 was prepared accurately.) Since health insurance in this case is not attributable to business income, it should not be used to reduce QBI.