You can legally start a business for tax write-offs, but the deductions only hold up if the venture is a real business in the eyes of the IRS. That means registering the right kind of entity, getting a federal Employer Identification Number, keeping business money separate from personal money, and operating with a genuine intent to make a profit. Skip those steps and the IRS can reclassify the whole thing as a hobby, disallow every deduction, and add penalties and interest on top.
Start With Profit Motive, Not Deductions
Section 183 of the Internal Revenue Code blocks deductions for any activity “not engaged in for profit.”1Office of the Law Revision Counsel. 26 USC 183 – Activities Not Engaged in for Profit If you build a venture whose only purpose is generating write-offs, you have already lost the argument. You don’t have to actually make money every year, but you do have to show that making money is your objective.
There is a safe harbor. If your activity produces a profit in three of the last five consecutive tax years, it is presumed to be a business. Horse breeding, training, and racing use a lower bar: two out of seven years.1Office of the Law Revision Counsel. 26 USC 183 – Activities Not Engaged in for Profit Meeting the threshold shifts the burden of proof to the IRS. Missing it doesn’t automatically kill your deductions, but it does mean you’ll be defending them.
When the safe harbor doesn’t settle it, Treasury Regulation 1.183-2 tells the IRS to look at the whole picture rather than tick boxes. The factors that carry the most weight in practice: whether you run the operation in a businesslike way with proper books and a separate bank account; whether you or your advisors have real expertise; whether you invest genuine time and effort; whether you change your approach when you lose money; your track record of income and losses; whether the activity is one you’d enjoy as a hobby anyway. The regulation warns that “greater weight is given to objective facts than to the taxpayer’s mere statement of his intent.”2eCFR. 26 CFR 1.183-2 – Activity Not Engaged in for Profit Defined Saying you meant to profit is not enough. Your behavior has to say it for you.
Pick a Structure Before You Register
The entity you choose sets your tax filings, your paperwork, and your personal liability exposure.
A sole proprietorship is the simplest. You report profits and losses on Schedule C attached to your personal Form 1040, and there is no state formation paperwork, though local permits may still apply.3Internal Revenue Service. About Schedule C (Form 1040), Profit or Loss From Business (Sole Proprietorship) The trade-off is zero liability protection. If the business is sued, your personal assets are on the line.
A Limited Liability Company (LLC) puts a legal wall between your personal assets and business debts. A single-member LLC is taxed like a sole proprietorship by default, so the return looks the same. Multi-member LLCs file Form 1065 as partnerships.4Internal Revenue Service. About Form 1065, U.S. Return of Partnership Income Formation happens at the state level, usually through the Secretary of State.
An S-Corporation can lower self-employment tax by splitting income between a reasonable salary (subject to payroll taxes) and distributions (not subject to payroll taxes). Owners performing services must pay themselves a reasonable salary before taking distributions. Skipping that step or setting the salary artificially low invites scrutiny.5Internal Revenue Service. Wage Compensation for S Corporation Officers S-Corps file Form 1120-S and carry more compliance overhead.
Most new side ventures start as sole proprietorships or single-member LLCs. The S-Corp election tends to pay off later, once the business earns enough that payroll tax savings outweigh the added accounting cost.
Register the Entity and Get an EIN
If you form an LLC or corporation, file articles of organization or incorporation with your state, usually through the Secretary of State’s online portal. Fees generally run from $50 to $500 depending on state and entity type. Online filings often process within a few business days; paper filings can take weeks.
Once the state recognizes your entity, apply to the IRS for a free Employer Identification Number. The online application at IRS.gov issues the nine-digit number immediately if everything checks out.6Internal Revenue Service. Get an Employer Identification Number It asks for the entity’s legal name, the responsible party’s name and Social Security Number, the type of entity, the principal business activity, and the expected number of employees.7Internal Revenue Service. Instructions for Form SS-4 The IRS never charges for an EIN. Any third-party website that does is charging you for something you can do yourself in minutes.
Then open a dedicated business bank account. Banks typically want your formation documents and EIN. Mixing personal and business funds is one of the first things the IRS checks in an audit, and doing it undercuts both your liability protection and your claim that you run the venture in a businesslike way.
Deduct Your Startup Costs in Year One
Money you spend before the business officially opens (market research, advertising, training, professional consultations) qualifies as startup expenditures under Section 195. You can deduct up to $5,000 of those costs in the year the business begins operating. That $5,000 phases out dollar-for-dollar once your total startup costs exceed $50,000, disappearing entirely at $55,000.8Office of the Law Revision Counsel. 26 USC 195 – Start-Up Expenditures
Anything above the first-year allowance amortizes over 180 months, starting the month the business launches. Spend $20,000 to get going, and you deduct $5,000 in year one plus $15,000 spread across the next 15 years.8Office of the Law Revision Counsel. 26 USC 195 – Start-Up Expenditures Many people assume pre-opening spending isn’t deductible at all and leave the deduction on the table.
Ongoing Write-Offs
Once the business is running, day-to-day costs are deductible on Schedule C if they are both “ordinary” (common in your industry) and “necessary” (helpful and appropriate for the business). Typical categories:
- Advertising and marketing, including website costs, ads, business cards, and promotional materials.
- Office supplies and postage.9Internal Revenue Service. Instructions for Schedule C (Form 1040)
- Rent for office space, co-working memberships, or equipment.
- Business insurance premiums.9Internal Revenue Service. Instructions for Schedule C (Form 1040)
- Utilities used for business. If you use your home phone, only the business portion beyond the base rate of your first line is deductible.
- Fees paid to accountants, lawyers, and consultants.
- Education, training, workshops, and publications that maintain or improve skills used in the business.
Documentation is what makes each deduction survive. A receipt alone is not enough. You need to be able to explain the business purpose. “Office supplies — $47.83 — printer paper and toner for client invoices” holds up. A bare credit card statement showing a charge at a supply store does not.
Home Office
Use part of your home exclusively and regularly for business, and you can deduct a portion of your housing costs. “Exclusive use” is strict. A guest room that doubles as an office fails the test. The area doesn’t need walls, but it does have to be a separately identifiable space used only for business.10Internal Revenue Service. Publication 587, Business Use of Your Home
Two calculation methods are available. The simplified method gives you $5 per square foot up to 300 square feet, capping the deduction at $1,500.11Internal Revenue Service. Simplified Option for Home Office Deduction The regular method applies the business-use percentage of your home to mortgage interest or rent, property taxes, utilities, insurance, and depreciation. It usually produces a larger deduction and requires far more record-keeping.
Vehicle Use
Business driving is deductible. Commuting from home to a regular workplace is not. For 2026, the standard mileage rate is 72.5 cents per mile.12Internal Revenue Service. IRS Sets 2026 Business Standard Mileage Rate If you own the vehicle, you have to elect the standard rate in the first year it’s available for business use, or you can’t use it later. For leased vehicles, whichever method you pick applies for the entire lease.
The alternative is tracking actual expenses (gas, insurance, repairs, depreciation, registration) and deducting the business-use percentage. Either method requires a contemporaneous mileage log with date, destination, business purpose, and miles for every trip. Vehicle deductions are among the most aggressively audited for small businesses, and rough estimates don’t survive.
The Qualified Business Income Deduction
Section 199A lets eligible owners of sole proprietorships, partnerships, and S-Corporations deduct up to 20% of their qualified business income. It comes off your taxable income and stacks on top of your ordinary business expense deductions. Income earned through a C-corporation or as a W-2 employee does not qualify.13Internal Revenue Service. Qualified Business Income Deduction
The deduction had been scheduled to sunset after December 31, 2025. The One Big Beautiful Bill Act, signed in July 2025, made it permanent. For 2026, the full 20% is available without limitation if taxable income falls below $201,750, or $403,500 for joint filers. Above those thresholds, the deduction phases out based on the wages the business pays and the value of qualified property, and it caps at the lesser of your QBI component or 20% of taxable income minus net capital gains.13Internal Revenue Service. Qualified Business Income Deduction
Self-Employment Tax and Quarterly Payments
Write-offs reduce income tax. They do not reduce self-employment tax, and that is the bill new business owners rarely see coming. If your net earnings hit $400, you owe self-employment tax at a combined 15.3%, covering both halves of Social Security (12.4%) and Medicare (2.9%).14Internal Revenue Service. Self-Employment Tax (Social Security and Medicare Taxes) The Social Security portion applies to the first $184,500 of combined wages and net self-employment income in 2026.15Social Security Administration. Contribution and Benefit Base Medicare has no cap. You calculate the tax on Schedule SE, and you can deduct half of what you pay as an adjustment to gross income.16Internal Revenue Service. Topic No. 554, Self-Employment Tax
Because nothing is withheld from your income, you pay estimated taxes quarterly. For the 2026 tax year, the deadlines are April 15, June 15, September 15, and January 15, 2027.17Taxpayer Advocate Service. Making Estimated Payments Missing them triggers an underpayment penalty. You avoid the penalty if the total tax due on your return is under $1,000, or if you paid at least 90% of your current-year liability or 100% of last year’s (whichever is less). If your prior-year adjusted gross income was over $150,000, that 100% threshold rises to 110%.18Internal Revenue Service. Underpayment of Estimated Tax by Individuals Penalty First-year owners frequently miscalculate because they forget to include self-employment tax.
Records and Annual Filings
Every deduction needs contemporaneous documentation, meaning you record the expense at or near the time it happens. Receipts, invoices, bank statements, and mileage logs all need to be preserved. Bookkeeping software satisfies the requirement and makes tax season considerably easier.
Your annual filing depends on your structure. Sole proprietors and single-member LLCs file Schedule C with Form 1040.3Internal Revenue Service. About Schedule C (Form 1040), Profit or Loss From Business (Sole Proprietorship) Partnerships and multi-member LLCs file Form 1065, which passes income and deductions through to partners on Schedule K-1.4Internal Revenue Service. About Form 1065, U.S. Return of Partnership Income S-Corporations file Form 1120-S with the same pass-through structure.
Late-filing penalties on partnership and S-Corp returns are steep: $255 per month or partial month, per partner or shareholder, for up to 12 months.19Internal Revenue Service. Failure to File Penalty A four-member LLC three months late on its partnership return owes $3,060 before it owes a dollar of tax. Most states also require annual or biennial reports to keep the entity in good standing, with fees that vary by state.
What Reclassification as a Hobby Costs
If the IRS decides your venture lacks a genuine profit motive, it reclassifies the activity under Section 183. You still owe income tax on every dollar the activity earned, but the deductions disappear. Under current law, hobby expenses cannot be used to offset even the hobby income itself.
On top of the disallowed deductions, the IRS typically adds a 20% accuracy-related penalty for negligence or substantial understatement of income.20Office of the Law Revision Counsel. 26 USC 6662 – Imposition of Accuracy-Related Penalty on Underpayments Interest accrues from the original due date, and the reclassification can reach back multiple years. A hobby finding in an audit does not stop at the year under review.
The protection is in the setup. Build the operation to satisfy the profit-motive factors from day one: separate bank account, clean books, real time and effort, adjustments when something isn’t working, and a paper trail behind every decision. A venture that looks like a business on paper and in practice rarely gets reclassified, even when it takes several years to reach profitability.