Schedule C
The part of Form 1040 where a sole proprietor or single-member LLC owner lists business income and expenses.
Sole proprietors report their business on Schedule C, Profit or Loss From Business, attached to Form 1040. The IRS Schedule C page says it's for income or loss from a business you operated as a sole proprietor.
A single-member LLC usually ends up on it as well. Publication 334 lets the owner use Schedule C as long as the owner is an individual and the LLC isn't engaged in farming.
Income at the top, ordinary and necessary expenses under it, net profit at the bottom. That profit gets taxed twice over. Once as ordinary income on Form 1040. Again as self-employment tax on Schedule SE. Paying yourself doesn't lower it, because owner draws aren't an expense. Take out $10,000 or $60,000 and the tax is figured on profit either way.
No separate federal tax, no separate return. For most owners with low profit, nothing is cheaper. Once profit climbs, self-employment tax on every dollar of it is what sends owners off to look at an S election.