You can reduce your taxable income with a side business by reporting it on Schedule C, where operating expenses come off revenue before anything reaches your Form 1040. A legitimate side business also opens deductions W-2 employees cannot touch: retirement plan contributions with high limits, self-employed health insurance premiums, half of your self-employment tax, and the qualified business income deduction. If the business runs at a loss and you meet the participation and at-risk rules, that loss can reduce the wages from your day job too. The savings are real, but every one of them depends on treating the venture like a business and keeping the paperwork to prove it.
The Business-vs-Hobby Line Comes First
Nothing below works if the IRS calls your activity a hobby. Hobby expenses cannot offset other income at all; they’re capped at hobby revenue, so a hobby can never generate a tax-reducing loss.1Office of the Law Revision Counsel. 26 U.S. Code 183 – Activities Not Engaged in for Profit
The IRS decides using nine factors in Treasury Regulation 1.183-2(b), looking at whether you keep real books, run a separate bank account, put in meaningful time, change tactics after losses, and rely on income from the activity. No single factor controls. There’s also a helpful presumption: if the business shows a net profit in three of five consecutive years, the IRS presumes a profit motive unless it can prove otherwise.2Internal Revenue Service. Audit Technique Guide: Activities Not Engaged in for Profit Activities that look like personal hobbies (photography, crafts, horse-related work) face extra scrutiny and need stronger documentation.
Ordinary Schedule C Deductions
Once the activity qualifies as a business, every ordinary and necessary operating cost comes off gross income on Schedule C. Ordinary means common in your trade; necessary means helpful and appropriate, not indispensable.3Office of the Law Revision Counsel. 26 U.S. Code 162 – Trade or Business Expenses
Typical write-offs include supplies, software subscriptions, web hosting, advertising, business insurance premiums, and professional fees paid to accountants or attorneys for the business.4Internal Revenue Service. IRS Form 1040 Schedule C – Profit or Loss From Business Travel qualifies when you’re away from your tax home long enough to need sleep or rest, and covers airfare, lodging, and 50% of meals; regular commuting between home and a fixed workplace doesn’t count.5Internal Revenue Service. Topic No. 511, Business Travel Expenses Courses and seminars are deductible when they maintain or improve skills you already use in the business; training for a new career is not.
Documentation carries the whole system. Keep receipts, invoices, and bank statements that show the amount, date, and business purpose. A dedicated business account and card make this simple. Records generally need to be kept at least three years from the date you filed.6Internal Revenue Service. How Long Should I Keep Records Assume every deducted dollar will have to be justified on paper.
Home Office
If part of your home is used exclusively and regularly as your principal place of business or as a place where you meet clients, a portion of housing costs is deductible. Exclusively is strict: the space cannot double as a guest room, playroom, or general living area.7Office of the Law Revision Counsel. 26 U.S. Code 280A – Disallowance of Certain Expenses in Connection With Business Use of Home
Two methods are available. The simplified method pays $5 per square foot up to 300 square feet, capping the deduction at $1,500.8Internal Revenue Service. Revenue Procedure 2013-13 – Safe Harbor Method for Determining Business Use of a Home The regular method applies your office’s percentage of total square footage to actual mortgage interest, property taxes, utilities, insurance, and repairs on Form 8829. It’s more work, and it usually produces a bigger deduction when housing costs are high.
Vehicle Use
Only the business portion of a personal vehicle is deductible, and you pick one of two methods. The standard mileage rate for 2026 is 72.5 cents per mile, which absorbs gas, insurance, depreciation, and wear.9Internal Revenue Service. IRS Sets Business Standard Mileage Rate The actual expense method deducts a business-use percentage of every real cost, including depreciation.
If you own the vehicle and want the standard mileage rate, elect it in the first year the car is available for business; after that you can switch year to year. For leased vehicles, if you start with the standard rate you have to stick with it for the entire lease.9Internal Revenue Service. IRS Sets Business Standard Mileage Rate Either method requires a mileage log with the date, destination, purpose, and miles. Vague or missing logs are one of the most common reasons the IRS denies vehicle deductions.
Writing Off Equipment in One Year
Long-lived business property such as computers, cameras, and furniture is normally depreciated over its useful life. Two rules let you skip that schedule. Section 179 lets you deduct the full purchase price of qualifying equipment in the year you place it in service, with a 2026 limit of $2,560,000, well beyond anything a side business will hit.10Internal Revenue Service. Publication 946 – How To Depreciate Property Recent legislation also restored 100% bonus depreciation for eligible new and used assets placed in service during the year. For most side businesses, a new laptop, desk, or specialized tool can be written off in full the year it’s bought.
Self-Employed Health Insurance
Self-employed people can deduct 100% of health, dental, and qualifying long-term care premiums for themselves, a spouse, and dependents. It’s an above-the-line deduction, so it reduces adjusted gross income whether or not you itemize.11Internal Revenue Service. Instructions for Form 7206
Two limits apply. The deduction cannot exceed the net earnings from the business under which the plan is established. And it’s unavailable for any month you were eligible to participate in a subsidized health plan through your employer or your spouse’s employer, even if you declined the employer plan and bought your own coverage. For side-hustlers with a W-2 job that offers health benefits, this deduction is often off the table.
Retirement Plans With High Contribution Limits
Self-employment income unlocks retirement accounts with limits far above a standard IRA, and contributions come off adjusted gross income before the standard or itemized deduction. Two plans dominate for side businesses.
SEP IRA
A Simplified Employee Pension IRA takes up to 25% of net self-employment earnings, with a 2026 cap of $72,000.12Internal Revenue Service. 2026 Amounts Relating to Retirement Plans and IRAs Only the employer side contributes. The main advantages are simplicity and timing: you can open and fund a SEP as late as your filing deadline including extensions, giving you until October 15 of the following year if you extend.13Internal Revenue Service. Retirement Plans for Self-Employed People
Solo 401(k)
The Solo 401(k) is for owners with no full-time employees other than themselves and a spouse. It stacks two contributions: an employee deferral up to $24,500 for 2026, plus an employer profit-sharing piece up to 25% of net self-employment earnings, with a combined ceiling of $72,000.14Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026 A catch-up of $8,000 applies at age 50, and a higher $11,250 catch-up applies for ages 60 through 63 under SECURE 2.0.
The Solo 401(k) also allows Roth treatment for the employee deferral, which won’t reduce this year’s taxes but grows and comes out tax-free. One timing catch: the plan must be established by December 31 of the tax year for you to make employee deferrals for that year, unlike the SEP. For someone with a high W-2 salary and moderate side income, the employee deferral alone can shelter $24,500 immediately.
Half of Your Self-Employment Tax
Net side-business earnings trigger self-employment tax: 12.4% Social Security plus 2.9% Medicare, for a combined 15.3%.15Social Security Administration. Contribution and Benefit Base The Social Security portion applies only up to $184,500 in combined wages and SE earnings for 2026. Medicare has no cap, and an extra 0.9% surtax kicks in above $200,000 (or $250,000 joint).
Half of the SE tax you owe is an above-the-line deduction on Form 1040, whether you itemize or not.16Internal Revenue Service. Topic No. 554, Self-Employment Tax On $50,000 of net self-employment income, the SE tax runs roughly $7,065, and about $3,532 of that comes back off AGI before income tax rates apply.
The Qualified Business Income Deduction
Section 199A lets eligible sole proprietors deduct up to 20% of net business income. It’s separate from expenses and retirement contributions, taken on the personal return, and reduces taxable income (not AGI, and not self-employment tax). Originally set to expire after 2025, recent legislation extended it into 2026 with adjustments to the phase-out ranges.
The full 20% is available when taxable income sits below the annual thresholds. Above them, the deduction phases out and can be limited by wages paid or property held. Certain service businesses, including consulting, law, accounting, and financial services, face additional restrictions at higher incomes. On $40,000 of net side-business income, the QBI deduction can shelter $8,000 from federal income tax with no work beyond filing.
Using a Business Loss Against Your W-2 Wages
When expenses exceed revenue, the loss can reduce the salary income you’re taxed on, but three rules stand between you and that result.
Material Participation
The loss is only “active,” and only usable against wages, if you materially participate. The clearest test is more than 500 hours of work in the activity during the year.17eCFR. 26 CFR 1.469-5T – Material Participation (Temporary) Six other tests exist, including being the only person substantially involved, or participating more than 100 hours when no one else participates more than you. Fail all seven and the loss is passive, meaning it can only offset passive income like rentals or limited-partnership earnings, not your paycheck.18Office of the Law Revision Counsel. 26 U.S. Code 469 – Passive Activity Losses and Credits Limited Keep a dated log of hours and tasks.
At-Risk Amount
Even with material participation, your deductible loss is capped at the amount you have at risk: cash invested, property contributed, and debt you’re personally liable for. Anything above that is suspended and carried forward until you add investment or the business earns income.19Office of the Law Revision Counsel. 26 U.S. Code 465 – Deductions Limited to Amount at Risk
Excess Business Loss Limit
Section 461(l) caps the amount of business loss you can apply against non-business income in one year. For 2026 the threshold is roughly $256,000 for single filers and $512,000 for joint filers. Anything over becomes a net operating loss carryforward to future years.20Internal Revenue Service. Instructions for Form 461, Limitation on Business Losses
Whatever survives all three rules flows from Schedule C to Form 1040 and cuts your AGI directly. A lower AGI can also expand eligibility for credits and deductions that phase out at higher incomes, including education credits, the child tax credit, and IRA deduction limits.
Don’t Forget Estimated Taxes
Side income has no automatic withholding. If you expect to owe at least $1,000 for the year after withholding and refundable credits, you generally have to make quarterly estimated payments, due April 15, June 15, September 15, and January 15 of the following year.21Internal Revenue Service. Estimated Tax
Miss them and an underpayment penalty accrues on each installment. Two safe harbors protect you: pay at least 90% of the current year’s tax, or 100% of the prior year’s tax (110% if last year’s AGI was over $150,000). The simplest fix for a first-year side business is often to raise the withholding on your W-2 through Form W-4. The IRS treats withholding as paid evenly across the year no matter when it’s actually taken out, so a single adjustment at your day job can keep you compliant without the quarterly filing process.