Schedule C is an IRS tax form (officially titled Profit or Loss from Business) that sole proprietors, freelancers, and single-member LLCs use to report self-employment income and deductible business expenses. It's filed as part of your personal Form 1040 and calculates your net profit, which becomes the basis for both your income tax and self-employment tax. You report all business revenue at the top, then subtract allowable expenses like supplies, advertising, professional services, home office costs, and mileage. The resulting net profit flows to your 1040 and is also used to calculate the self-employment tax owed on Schedule SE. If your business had a net loss, it can often offset other income on your return.