What this line means
Your final business bottom line: line 29 (tentative profit) minus line 30 (business use of home deduction). If positive, this is your net profit — it flows to Form 1040 line 8 as income and to Schedule SE for self-employment tax. If negative, it is a net loss that reduces your other income on Form 1040. This single number determines how much income tax and self-employment tax you owe on your business.
Does this apply to you?
- Every Schedule C filer completes this line — it is the final result of the entire form
- A positive number means your business made money and you owe tax on it
- A negative number means your business lost money and the loss offsets other income
Easy to overlook
Net profit triggers self-employment tax on top of income tax Net profit is not just subject to regular income tax. It also triggers self-employment tax (15.3% for the first $176,100 of combined earnings in 2025, then 2.9% above that). 1 SE tax is calculated on 92.35% of net profit (not the full amount) because the IRS adjusts for the employer-equivalent portion. A sole proprietor with $80,000 net profit owes roughly $11,300 in self-employment tax before income tax even starts. This catches first-time self-employed filers off guard. IRS Schedule SE — Self-Employment Tax
Net profit may qualify for the 20% QBI deduction Under Section 199A, sole proprietors can deduct up to 20% of qualified business income directly from taxable income. 2 If your Schedule C net profit is $100,000 and you qualify, you deduct $20,000 before income tax is calculated. The deduction phases out for specified service trades (law, medicine, consulting) above $197,300 single / $394,600 MFJ in 2025. This deduction is claimed on Form 1040 line 13, not on Schedule C itself. IRS Form 8995 Instructions — Qualified Business Income Deduction
A loss limits several other deductions If your business shows a net loss, the IRS applies the excess business loss limitation ($313,000 for single filers, $626,000 for married filing jointly in 2025). 3 Losses beyond these limits cannot offset other income in the current year — they become net operating loss carryforwards. Also, repeated losses across multiple years trigger the hobby loss rule, where the IRS may reclassify your business as a hobby and deny all deductions. IRS Schedule C instructions — Line 31
Watch out for this
Not making quarterly estimated tax payments on net profit. As a sole proprietor, no employer withholds taxes from your business income. You must make quarterly estimated payments (Form 1040-ES) covering both income tax and self-employment tax on this amount. Failing to do so results in an underpayment penalty, even if you pay the full amount when you file.
Footnotes
-
IRS Schedule SE (Form 1040) Instructions. https://www.irs.gov/instructions/i1040sse ↩
-
IRS Form 8995 Instructions, Qualified Business Income Deduction (Section 199A). https://www.irs.gov/instructions/i8995 ↩
-
IRS Schedule C (Form 1040) Instructions, Line 31. https://www.irs.gov/instructions/i1040sc ↩