Why it matters to small-business owners

Sole proprietors, single-member LLCs, and gig workers report their business activity on a separate schedule (Schedule C, E, or F) but the bottom line flows to Form 1040, where it is combined with W-2 wages, interest, dividends, capital gains, and other income to determine total tax. Because business income is intertwined with the personal return, small-business owners must coordinate Schedule C, Schedule SE, Schedule 1 adjustments, and the QBI deduction (Form 8995 or 8995-A) on the same Form 1040 each year.

Schedules that ride along

Schedule 1 handles additional income (including business profit) and adjustments to income (such as the deductible part of SE tax, the self-employed health insurance deduction, and SEP/SIMPLE/qualified plan contributions). Schedule 2 reports SE tax and other "additional" taxes. Schedule 3 reports nonrefundable and refundable credits. Schedules A, B, C, D, E, and F report itemized deductions, interest and dividends, business income, capital gains, rental income, and farm income respectively.

Standard deduction or itemize

Most taxpayers take the standard deduction, but business owners who pay significant state and local taxes, mortgage interest, or charitable contributions should run the math on Schedule A. Note that business expenses do not appear on Schedule A — they belong on Schedule C and reduce both income tax and self-employment tax — so the choice between standard and itemized only affects personal expenses.

Filing deadlines and extensions

Form 1040 is due April 15. An automatic six-month extension to October 15 is available by filing Form 4868, but the extension is for the return only — any tax owed must still be paid by April 15 to avoid interest and the failure-to-pay penalty. Self-employed filers should also calendar the four estimated tax payment dates: April 15, June 15, September 15, and January 15 of the following year.

Common pitfalls

The most common errors on a small-business 1040 are forgetting to file Schedule SE on profit of $400 or more, missing the QBI deduction, and double-counting health insurance premiums on both Schedule C and the self-employed health insurance line on Schedule 1.