| Chapter 18 - Sole Proprietorships/18.1-schedule-c-se-tax.md | Schedule C, SE Tax, QBI, Estimated Tax |

Key concepts: Schedule C income/expense reporting, SE tax (net profit × 92.35% × 15.3%), 50% SE tax deduction, SE health insurance deduction (limited to net profit), QBI deduction (20%, income thresholds $197,300/$394,600), SSTB phase-out, estimated tax (Q1/Q2/Q3/Q4 due dates), safe harbor (90% current or 100%/110% prior year), at-risk rules, passive activity rules.

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