A self-employed person can deduct half of the self-employment taxes paid, which are the Social Security and Medicare taxes owed. An employee has 7.65% of their salary withheld for these taxes, and then the employer matches those taxes. A self-employed person pays both halves, or 15.3%, on their income. When calculating the QBI deduction, you deduct 50% of the self-employment taxes against your net locum tenens income to come up with the income eligible for the QBI deduction. If you contribute to a retirement plan, you would deduct that before calculating the QBI deduction as well.