To write off business expenses as a sole proprietor, you claim each ordinary and necessary cost of running your business on Schedule C, keep documentation that proves the amount and business purpose, and pay the resulting tax in quarterly installments. Every dollar you deduct cuts both your income tax and your self-employment tax, which is why careful expense tracking pays back more than almost anything else you do in a small business.
The sections below walk through which costs qualify, how to handle the ones that mix business and personal use, the deductions that sit outside Schedule C, and the records you need to keep the write-offs if the IRS asks.
The Rule That Decides What You Can Deduct
Internal Revenue Code Section 162 permits deducting expenses that are “ordinary and necessary” for your trade or business.1Office of the Law Revision Counsel. 26 USC 162 – Trade or Business Expenses Ordinary means common and accepted in your line of work. Necessary means helpful and appropriate, not absolutely essential. The cost also has to be reasonable in amount.
Personal, living, and family expenses are never deductible.2Office of the Law Revision Counsel. 26 USC 262 – Personal, Living, and Family Expenses When something serves both purposes, like a cell phone, an internet connection, or a car, only the business portion qualifies, and you need a defensible way to split the cost. A usage log or time-based allocation works. The IRS treats the first landline phone in your home as personal no matter how much business you conduct on it.
Timing matters too. Rent, supplies, advertising, and similar costs used up within the year get deducted immediately. Purchases that create a lasting asset, like equipment or vehicles, are spread over the asset’s useful life through depreciation unless you elect one of the accelerated methods below.
Everyday Operating Expenses
Most of what you spend running a sole proprietorship falls into straightforward categories that go directly on Schedule C and are fully deductible in the year you pay them.3Internal Revenue Service. Instructions for Schedule C (Form 1040) – 2025
Office supplies (paper, ink, postage, printer cartridges), software subscriptions, cloud storage, and small equipment purchases too minor to depreciate go on line 18. If you sell physical products, the cost of goods purchased for resale goes in Part III as cost of goods sold instead. Businesses with average annual gross receipts of $30 million or less can skip formal inventory accounting and treat those costs as non-incidental materials and supplies deducted when used.4Internal Revenue Service. Publication 538 – Accounting Periods and Methods
Advertising and marketing costs cover website development, social media and search ads, print materials, business cards, trade show fees, and promotional merchandise. The spending must aim at generating business income; costs that mainly enhance your personal reputation don’t qualify.
Professional fees paid to attorneys, accountants, and consultants for business work are deductible in the year the work is performed and paid. Tax preparation fees tied to your Schedule C count; the personal portion of your return doesn’t.
Rent for an office, warehouse, storefront, or leased equipment is fully deductible, along with utilities for a dedicated commercial space. Internet and phone bills that also serve personal use get split by actual usage.
Business insurance premiums — general liability, professional malpractice, property coverage on business equipment, business interruption — go on Schedule C. Self-employed health insurance follows different rules and is covered further down.
Travel away from your tax home overnight for business is deductible: airfare, lodging, rental cars, taxis. Daily commuting between home and a regular workplace never counts. Mixed business-and-personal trips have to be separated so only the business portion is claimed. Records should capture dates, destination, purpose, and amount.
Interest on business credit cards, commercial loans, and lines of credit used for business is deductible. Interest on a personal card is deductible only to the extent it relates to business charges. Points paid on a business loan get spread over the loan’s life. Most sole proprietors are well under the gross receipts threshold that triggers the business interest limitation, so business interest is typically fully deductible.
Licenses, permits, and regulatory fees required to operate legally are deductible in the year paid. So are business bank account fees, credit card processing charges, payment gateway fees, and merchant service fees.
Bad debts have a narrower rule. If you use accrual accounting and a client never pays an invoice you already reported as income, you can deduct the uncollectible amount.5Internal Revenue Service. Topic No. 453 – Bad Debt Deduction Cash-method sole proprietors generally can’t, because the unpaid amount was never counted as income to begin with.
Business Meals at 50 Percent
Business meals are deductible at 50% of the actual cost, including tax and tip.6Internal Revenue Service. Tax Cuts and Jobs Act – Businesses You or an employee must be present, and the meal has to involve a business discussion with a client, customer, or similar contact. It can’t be lavish. Record the full cost and claim 50% on Schedule C, line 24b. The temporary 100% deduction for restaurant meals in 2021 and 2022 has expired.
Meals provided to employees at company-wide events like a holiday party are generally 100% deductible, but the typical sole proprietor taking a client to lunch is capped at 50%.
Home Office
If you use a specific area of your home exclusively and regularly as your principal place of business or a space to meet clients, you can deduct a share of your housing costs.7Internal Revenue Service. Simplified Option for Home Office Deduction “Exclusively” is strict. A guest bedroom that doubles as your office doesn’t qualify unless it’s used only for business during the period you claim.
Two methods are available:
- Simplified method. Deduct $5 per square foot of home office, up to 300 square feet, for a maximum of $1,500. No tracking of actual home expenses, no Form 8829.
- Regular method. Calculate actual expenses (mortgage interest, property taxes, utilities, insurance, repairs) and multiply by the percentage of your home used for business. File Form 8829 and depreciate the business portion of the home over 39 years.
The regular method often produces a larger deduction, especially with high housing costs or a sizable dedicated workspace. The trade-off is that when you sell the home, depreciation claimed after May 6, 1997 is taxed at a 25% recapture rate, even if the rest of the gain qualifies for the home sale exclusion. The simplified method avoids that. Either way, the deduction lands on Schedule C, line 30.
Vehicle Use
You can deduct the cost of using a personal vehicle for business, but you need a mileage log showing the date, destination, business purpose, and miles for each trip. Commuting between home and a regular workplace is not business mileage. If your home office is your principal place of business, trips from home to client sites do count.
You pick between two methods:
- Standard mileage rate. For 2026, the IRS rate is 70 cents per business mile, which covers gas, maintenance, insurance, and depreciation. Parking and tolls are deductible on top of the mileage rate.8Internal Revenue Service. Standard Mileage Rates
- Actual expense method. Track gas, oil, repairs, tires, insurance, registration, and lease payments, then multiply by your business-use percentage. You can also depreciate the business portion of the vehicle’s cost, subject to annual passenger-auto limits.9Internal Revenue Service. Rev. Proc. 2026-15 – Depreciation Limitations for Passenger Automobiles
One lock-in rule to know before you choose. If you start with the standard mileage rate in the first year you use a vehicle for business, you can switch to actual expenses later. If you start with actual expenses, you’re stuck with that method for the life of that vehicle. Run the numbers both ways the first year.
Buying Equipment: Depreciation, Section 179, and Bonus Depreciation
When you buy equipment, furniture, machinery, or other business assets that will last more than a year, you generally recover the cost through depreciation under the Modified Accelerated Cost Recovery System.10Internal Revenue Service. Instructions for Form 4562 – Depreciation and Amortization (2025) A computer is five-year property. Office furniture is seven-year property. Nonresidential real property runs 39 years. All of it is calculated on Form 4562 and reported on Schedule C, line 13.
Two accelerated options let you skip the multi-year schedule:
- Section 179 expensing. You can deduct the full purchase price of qualifying equipment and software in the year it’s placed in service, up to $2,560,000 for 2026. The limit phases out once total qualifying purchases exceed $4,090,000. The Section 179 deduction can’t exceed your net business income for the year; anything above that carries forward.
- Bonus depreciation. Eligible property placed in service in 2026 qualifies for 100% bonus depreciation under recent legislation, letting you write off the entire cost in year one. Unlike Section 179, bonus depreciation can create or increase a net operating loss. It applies to new and used property as long as it’s new to you.
For most sole proprietors buying a laptop, a delivery van, or shop equipment, Section 179 alone covers the full cost. Bonus depreciation matters more for larger purchases or when Section 179 would be capped by net income.
If You Just Started the Business
Costs paid before your business opened, such as market research, pre-launch advertising, training, and consultations, get special treatment. You can deduct up to $5,000 of startup expenses in the year the business begins operating, but that $5,000 shrinks dollar-for-dollar once total startup costs exceed $50,000.11Office of the Law Revision Counsel. 26 USC 195 – Start-up Expenditures Anything above the immediate deduction is spread evenly over 180 months starting with the month you open. Equipment and inventory follow their own rules and are not part of the startup pool.
Deductions That Sit Above Schedule C
Several deductions available to sole proprietors are not on Schedule C itself. They appear on Schedule 1 of Form 1040 and reduce your adjusted gross income, which can also unlock benefits that phase out at higher AGI.
Half of Your Self-Employment Tax
As a sole proprietor, you pay both the employer and employee shares of Social Security and Medicare, a combined 15.3% (12.4% Social Security on net earnings up to $184,500 in 2026, plus 2.9% Medicare on all net earnings).12Social Security Administration. Contribution and Benefit Base The tax is calculated on Schedule SE against 92.35% of your net self-employment income. Half of what you owe is then deducted on Schedule 1.13Internal Revenue Service. Self-Employment Tax (Social Security and Medicare Taxes)
Self-Employed Health Insurance
If you pay your own health insurance and aren’t eligible for a subsidized plan through a spouse’s or another employer, you can deduct 100% of premiums for medical, dental, and vision coverage for yourself, your spouse, and your dependents. The deduction goes on Schedule 1, line 17, calculated on Form 7206.14Internal Revenue Service. Instructions for Form 7206 – Self-Employed Health Insurance Deduction (2025) It cannot exceed the net self-employment income from the business that established the plan.
Retirement Contributions
Sole proprietors have two common options that significantly cut taxable income:
- SEP IRA. Contribute up to 25% of net self-employment earnings (after the SE tax deduction), maxing out at $72,000 for 2026. Because of how the math works after removing the SE tax deduction, the effective rate is closer to 20% of net profit. No annual filing requirement.15Internal Revenue Service. SEP Contribution Limits (Including Grandfathered SARSEPs)
- Solo 401(k). Defer up to $24,500 as the employee in 2026, plus contribute up to 25% of net self-employment earnings as the employer, for a combined ceiling of $72,000 if you’re under 50. Catch-up contributions add $8,000 if you’re 50 to 59 or 64 and older, or $11,250 if you’re 60 to 63. More paperwork than a SEP but higher contribution potential at lower income levels.16Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026, IRA Limit Increases to $7,500
Both are deducted on Schedule 1. For a sole proprietor with strong net income, retirement contributions are often the single largest deduction outside Schedule C itself.
Qualified Business Income
Under Section 199A, sole proprietors can deduct up to 20% of qualified business income on their personal return.17Internal Revenue Service. Qualified Business Income Deduction The deduction is generally straightforward when taxable income stays under $201,750 ($403,500 married filing jointly) for 2026. Above those thresholds the calculation gets more complex, and businesses in law, accounting, health care, consulting, and financial services face phase-outs that can eliminate the deduction once taxable income passes $276,750 ($553,500 joint). The deduction was set to expire after 2025 but has been extended under recent legislation.
Records That Make the Deductions Stick
No deduction survives without documentation. If the IRS audits and you can’t produce records, the deduction gets disallowed, regardless of whether the expense was real. The burden of proof is on you.
Your records need to establish four things for each expense: the amount, when and where it happened, the business purpose, and, for meals, the business relationship of anyone involved. Receipts, bank and credit card statements, invoices, and contracts all qualify. For travel, meals, and vehicle use, contemporaneous records created at or near the time of the expense carry more weight than anything reconstructed months later.
Electronic records are equivalent to paper originals, provided they’re complete, legible, and retrievable on demand.18Internal Revenue Service. Revenue Procedure 97-22 – Electronic Records Scanning receipts with a phone app the day you get them and storing them in accounting software is the practical standard now. Paper fades. Digital copies don’t.
Keep records at least three years after filing the return or its due date, whichever is later, which matches the IRS’s general audit statute.19Internal Revenue Service. How Long Should I Keep Records? If you underreported gross income by more than 25%, the window is six years. If the return was fraudulent or never filed, there’s no time limit.20Internal Revenue Service. Publication 583 – Starting a Business and Keeping Records Six years is the safer default.
Weak substantiation costs more than the deduction. An accuracy-related penalty of 20% applies to the resulting underpayment, and interest accrues from the original due date.21Office of the Law Revision Counsel. 26 USC 6662 – Imposition of Accuracy-Related Penalty on Underpayments
Paying the Tax as You Go
No employer is withholding taxes from your income, so the IRS expects quarterly estimated tax payments through Form 1040-ES if you expect to owe $1,000 or more on your return.22Internal Revenue Service. 2026 Form 1040-ES – Estimated Tax for Individuals
The 2026 due dates are:
- First quarter: April 15, 2026
- Second quarter: June 15, 2026
- Third quarter: September 15, 2026
- Fourth quarter: January 15, 2027
You can skip the January payment if you file your 2026 return and pay the balance by February 1, 2027. Miss a deadline and you’ll owe an underpayment penalty calculated as interest on the shortfall.
Two safe harbors protect you: pay at least 90% of the current year’s tax, or pay 100% of the prior year’s tax (110% if prior-year AGI exceeded $150,000).23Internal Revenue Service. Underpayment of Estimated Tax by Individuals Penalty Basing payments on last year’s tax and adjusting as income changes is the simplest approach.
How It All Lands on Schedule C
Schedule C, Profit or Loss From Business, is where the deductions come together. Part I captures gross income. If you sell products, Part III calculates cost of goods sold. Part II is the main expense section with a designated line for each category: office expenses on line 18, depreciation on line 13, business meals at 50% on line 24b, vehicle expenses on line 9, home office on line 30.3Internal Revenue Service. Instructions for Schedule C (Form 1040) – 2025
Line 31 gives you net profit or loss. That figure flows to Schedule 1, line 3, where it joins your total income,24Internal Revenue Service. 2025 Schedule C (Form 1040) – Profit or Loss From Business and it also feeds Schedule SE for the self-employment tax calculation.25Internal Revenue Service. Topic No. 554 – Self-Employment Tax Because each Schedule C deduction reduces both income tax and self-employment tax, the effective savings from a single business write-off are larger than most people expect. The IRS flags returns whose expense-to-income ratios deviate sharply from industry norms, so organized backup for each line is the best protection if the numbers ever get a second look.