IRS Publication 334: Tax Guide for Small Business
IRS Publication 334 is the definitive tax guide for small business owners and self-employed individuals. It covers everything from how to report business income on Schedule C to which expenses are deductible, how depreciation works, when the home office deduction applies, and what employment taxes you owe if you have employees. If you are a sole proprietor, independent contractor, freelancer, or gig worker, Publication 334 is the standard the IRS uses to evaluate your return — and it is the standard you will be measured against in an audit.
Key Topics Covered in Publication 334
Schedule C — Profit or Loss From Business
Schedule C is the core form for reporting business income and expenses. Publication 334 walks through every line: gross receipts, returns and allowances, cost of goods sold, gross profit, and all expense categories. It explains what qualifies as business income (cash, checks, 1099-NEC, 1099-K, barter, and digital payments) and how to properly categorize each revenue stream on your return.
Self-Employment Tax (Schedule SE)
Self-employment tax is the self-employed equivalent of Social Security and Medicare taxes. At 15.3% (12.4% Social Security plus 2.9% Medicare), it is one of the largest tax obligations for small business owners. Publication 334 explains how to calculate SE tax, the Social Security wage base cap, the additional 0.9% Medicare surtax on high earners, and the deduction for one-half of SE tax on your 1040.
Business Expenses — What Is Deductible
Publication 334 defines the ordinary and necessary standard for business expenses. It covers advertising, insurance, interest, legal and professional fees, office expenses, rent, repairs and maintenance, supplies, taxes and licenses, travel and meals, utilities, and wages paid to employees. The publication also addresses mixed-use expenses and documentation requirements for substantiating deductions.
Depreciation, Section 179, and Bonus Depreciation
Business assets with a useful life beyond one year must be depreciated rather than expensed in a single year. Publication 334 covers MACRS depreciation, the Section 179 deduction (allowing up to $1,220,000 for 2026 in immediate expensing of qualifying property), bonus depreciation rules, listed property restrictions, and how to correct depreciation errors from prior years.
Home Office Deduction
Publication 334 details the requirements for claiming a home office: exclusive and regular use, principal place of business, and the two calculation methods (regular method using actual expenses and Form 8829, or the simplified method at $5 per square foot up to 300 square feet). It also addresses special rules for daycare providers and storage of inventory.
Common Issues & Correction Strategies
Hobby Loss Rules (IRC 183)
The IRS scrutinizes businesses that report losses year after year. If your activity is not engaged in for profit, deductions are limited to hobby income — you cannot deduct losses against other income. Publication 334 explains the 9 factors the IRS uses to determine profit motive. If the IRS reclassified your business as a hobby, you can contest it by demonstrating a profit-seeking operation with proper records.
Estimated Tax Penalties
Small business owners and self-employed individuals must pay estimated taxes quarterly (Form 1040-ES). Missing deadlines or underpaying triggers the underpayment penalty. Publication 334 covers the safe harbor rules: pay 100% of last year's tax (110% if AGI exceeds $150,000) or 90% of current year tax. If you already owe penalties, you may qualify for a waiver or penalty abatement.
Business Vehicle Expense Deductions
Publication 334 distinguishes between the standard mileage rate and the actual expense method for deducting vehicle costs. It also covers the strict contemporaneous recordkeeping requirements — mileage logs, dates, business purpose, and odometer readings. IRS auditors routinely disallow vehicle deductions with inadequate documentation. Reconstructing logs from calendar entries, appointment records, and GPS data can salvage disallowed deductions.
Employee vs. Independent Contractor Misclassification
Treating a worker as an independent contractor when the IRS would classify them as an employee is one of the costliest small business mistakes. Publication 334 references the common law test: behavioral control, financial control, and the relationship of the parties. Misclassification can trigger back employment taxes, penalties under Section 3509, and Form SS-8 determinations. The IRS Voluntary Classification Settlement Program (VCSP) offers a path to resolve misclassification with reduced penalties.