The best S corp write-offs cluster in a handful of categories that together decide how much profit reaches the owner’s personal return: a reasonable owner salary paid through payroll, health insurance and retirement contributions, the qualified business income deduction, ordinary operating expenses, immediate expensing of equipment, and carefully documented travel, meal, vehicle, and home office costs. Because the S corporation itself pays no federal income tax, every deductible dollar reduces what flows through on the K-1 and lands on Form 1040.
Owner Salary: The Deduction That Shapes All the Others
The salary an S corp pays its owner-employee is fully deductible by the company, and it is also the number the IRS looks at first. Any officer who performs more than minor services must be paid a W-2 salary reflecting fair market value for the work.1Internal Revenue Service. S Corporation Employees, Shareholders and Corporate Officers That salary is subject to Social Security and Medicare tax on both sides of the payroll ledger.
What makes the structure attractive is what happens after the salary is set. Profit left over after reasonable compensation can be distributed to the shareholder without triggering Social Security or Medicare tax. Set the salary too low and the IRS can recharacterize distributions as wages, adding back employment taxes plus interest and penalties. The agency weighs the owner’s training, duties, hours, and comparable pay in similar businesses when it looks at whether the salary is defensible.2Internal Revenue Service. S Corporation Compensation and Medical Insurance Issues
Salary matters for another reason too. Retirement plan contributions and the QBI calculation both depend on W-2 wages, so an artificially low salary shrinks other write-offs down the line.
Health Insurance and Other Benefits for the Owner
Health insurance premiums the S corp pays for a shareholder who owns more than 2% of the stock get special handling. The company deducts the premiums, but the amount must be added to the owner’s W-2 in Box 1 for income tax purposes. It stays out of Boxes 3 and 5, so no Social Security or Medicare tax applies.2Internal Revenue Service. S Corporation Compensation and Medical Insurance Issues
The owner then claims the self-employed health insurance deduction on their personal return, which offsets the income inclusion. The company gets the deduction, the owner effectively pays no tax on the benefit, and coverage must be established through the S corp for the treatment to work.
Group-term life insurance follows a similar add-to-W-2 pattern, though it is included for Social Security and Medicare purposes as well.3Internal Revenue Service. Publication 15-B (2026), Employer’s Tax Guide to Fringe Benefits Health reimbursement arrangements and QSEHRAs are not available to 2% shareholders at all.
Retirement Plan Contributions
Retirement contributions are among the highest-leverage deductions available to an S corp because the money reduces taxable income while building the owner’s personal savings tax-deferred. Contributions are calculated on W-2 wages, not distributions.4Internal Revenue Service. Retirement Plan FAQs Regarding Contributions – S Corporation
Solo or Small-Business 401(k)
For 2026, an owner-employee can defer up to $24,500 of salary as an employee contribution.5Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026, IRA Limit Increases to $7,500 The S corp can add employer matching or profit-sharing contributions on top, with combined employee and employer contributions capped at $72,000. Owners 50 and older can add a $7,500 catch-up. Both employer contributions and salary deferrals processed through payroll are deductible.
SEP IRA
The S corp can contribute up to 25% of the owner’s W-2 compensation, capped at $72,000 for 2026.6Internal Revenue Service. SEP Contribution Limits (Including Grandfathered SARSEPs) Contributions are entirely employer-side, with no employee deferral, which makes administration simple.
SIMPLE IRA
The 2026 employee deferral limit is $16,500, with a catch-up for those 50 and older. The company must either match employee contributions dollar-for-dollar up to 3% of compensation or make a 2% nonelective contribution for all eligible employees. Everything the company pays in, along with the deferrals it processes, is deductible.
The Qualified Business Income Deduction
Section 199A lets eligible shareholders deduct up to 20% of their qualified business income on their personal return. It does not touch Form 1120-S. It applies at the individual level after the K-1 flows through.7Internal Revenue Service. Qualified Business Income Deduction
The owner’s reasonable salary is not QBI. Only the pass-through profit qualifies, which creates a tension worth planning around: a higher salary means more employment tax but a smaller QBI base, while a lower salary shrinks employment tax but invites IRS scrutiny. Most owners set compensation at a genuinely defensible number and let the QBI deduction do its work on what remains.
Section 199A was originally set to expire at the end of 2025 but was extended by the One, Big, Beautiful Bill signed into law in 2025. Above certain taxable income thresholds, the deduction is limited by W-2 wages the S corp pays and the cost of depreciable business property. Specified service businesses like law firms, medical practices, and consulting companies face additional phase-outs. Starting in 2026, those phase-out ranges widen to $150,000 for joint filers and $75,000 for other filers before the deduction is eliminated for service businesses.
Everyday Operating Expenses
The general rule for any business deduction is that the expense must be ordinary and necessary under Section 162, meaning common in the industry and helpful to the business.8Office of the Law Revision Counsel. 26 USC 162 – Trade or Business Expenses That covers most of what keeps the doors open.
Rent, utilities, and maintenance for office or retail space are fully deductible. So are supplies, postage, printing, and routine repairs. Professional fees paid to attorneys, accountants, and consultants come off in the year paid or incurred. Advertising, marketing, website hosting, and social media costs deduct with no percentage limit. Business insurance premiums, including liability, property, and professional coverage, are deductible, as is interest on loans used for business operations. Interest on debt used to generate tax-exempt income is not.
Documentation decides whether these expenses survive an audit. Keep invoices, bank statements, and receipts that tie each cost to a business purpose, and categorize the expense correctly on Form 1120-S.
Section 179 and Bonus Depreciation on Equipment
When the S corp buys equipment, vehicles, or other property meant to last more than a year, the cost would ordinarily be spread over the asset’s useful life. Two provisions let the company deduct most or all of that cost right away.
Section 179
Section 179 lets the S corp expense qualifying property in the year it is placed in service. For 2026, the maximum is $1,250,000, adjusted annually for inflation.9Office of the Law Revision Counsel. 26 USC 179 – Election to Expense Certain Depreciable Business Assets Qualifying property includes machinery, equipment, computers, office furniture, and certain improvements to nonresidential buildings. The deduction phases out dollar-for-dollar once total qualifying purchases in the year cross an inflation-adjusted investment threshold.
Section 179 cannot create or increase a net loss. It can only offset active business income, with any excess carrying forward. The election is made on Form 4562.
Bonus Depreciation
The One, Big, Beautiful Bill restored 100% bonus depreciation as a permanent provision for qualifying property acquired after January 19, 2025.10Internal Revenue Service. Treasury, IRS Issue Guidance on the Additional First Year Depreciation Deduction Amended as Part of the One, Big, Beautiful Bill An S corp buying qualifying property in 2026 can deduct the full cost in year one, with no dollar cap and no taxable income limitation. Unlike Section 179, bonus depreciation can create or increase a net loss, which makes it useful for companies in early growth or heavy expansion.
One transitional detail matters: property acquired before January 20, 2025, but placed in service in 2026 gets only 20% bonus depreciation under the old phase-down schedule. Contract dates and order dates should be documented for any large purchase near that line. Taxpayers can also elect a lower bonus percentage if spreading the deduction across years fits the plan better.
Travel, Meals, and Vehicles
These categories draw heavy IRS attention because personal use blends in easily. Contemporaneous records are essential.
Business Travel
Travel expenses incurred while the owner is away from their tax home overnight for business are deductible: airfare, hotel, ground transportation, baggage fees, dry cleaning, and related tips.11Internal Revenue Service. Topic No. 511, Business Travel Expenses Records must show the amount, date, location, and business purpose for each expense, captured at or near the time it was incurred.
Business Meals
Business meals are 50% deductible. The meal cannot be lavish, and the owner or another company representative must be present.12Internal Revenue Service. Temporary 100-Percent Deduction for Business Meal Expenses Notice 2021-25 Track the amount, date, place, attendees, their business relationship, and the topic discussed. The temporary 100% restaurant deduction from 2021 and 2022 has expired. Entertainment expenses remain fully nondeductible, though food served at an entertainment event still qualifies for the 50% deduction if it is invoiced or receipted separately.11Internal Revenue Service. Topic No. 511, Business Travel Expenses
Vehicles
The company can use either the standard mileage rate or the actual expense method. For 2026, the standard rate is 72.5 cents per mile for business use.13Internal Revenue Service. 2026 Standard Mileage Rates A mileage log with date, destination, odometer readings, and business purpose is required.
The actual expense method deducts the business-use percentage of gas, oil, repairs, tires, insurance, registration, lease payments, garage rent, and depreciation.14Internal Revenue Service. Publication 463 (2025), Travel, Gift, and Car Expenses It usually beats the standard rate on expensive vehicles or in high-fuel-cost years, but every receipt has to be kept. A mileage log is still needed to prove the business-use percentage.
Home Office
A home office deduction is available when a specific part of the home is used exclusively and regularly as the principal place of business. Exclusive means the space is not doubling as a guest room or a den. The simplified method allows $5 per square foot up to 300 square feet, for a maximum of $1,500 per year.15Internal Revenue Service. Simplified Option for Home Office Deduction
The regular method uses a business-use percentage against actual expenses: mortgage interest or rent, utilities, insurance, repairs, and depreciation. It usually produces a larger number when the office is sizable, but it takes more record-keeping and may trigger depreciation recapture when the home is sold. For S corp owners specifically, the cleanest approach is often to have the company reimburse the owner for home office costs under an accountable plan.
Accountable Plans and the Records That Protect Every Deduction
An accountable plan is a written company policy for reimbursing the owner-employee for out-of-pocket business expenses. Done right, reimbursements are excluded from the owner’s income, stay off the W-2, and are exempt from employment taxes, while the S corp deducts the reimbursed amounts as ordinary business costs.
Three elements are required. The expense must have a clear business connection. The owner must substantiate it with receipts within a reasonable time. Any excess reimbursement must be returned to the company within a reasonable time. Miss any one of those and the entire reimbursement becomes taxable wages.
A few other habits keep the rest of the return defensible:
- Keep separate bank accounts and credit cards for the S corp. Commingling funds is the fastest way to have the IRS question whether the corporate structure is real.
- Stick to one accounting method year over year. Cash-basis companies deduct when paid, accrual-basis when the obligation arises, and switching without IRS permission triggers adjustments.
- Classify expenses correctly. A $30,000 machine is not office supplies; it is capital property that needs a proper Section 179 or bonus depreciation election.
A Boundary Worth Knowing: Losses Are Capped by Basis
Any of these deductions can push the S corp to a net loss, but the owner can only deduct losses up to their stock basis plus any direct loans they have made to the company.16Office of the Law Revision Counsel. 26 USC 1366 – Pass-Thru of Items to Shareholders Losses over that combined amount carry forward until basis is available again.
Stock basis begins with what the owner paid or contributed, rises with income and additional contributions, and falls with losses, distributions, and nondeductible expenses. Debt basis comes only from direct shareholder loans to the company. Bank loans to the S corp, even with a personal guarantee, do not create debt basis. Owners claiming a loss must file Form 7203 with their personal return to show they have the basis to support it.17Internal Revenue Service. Instructions for Form 7203 Even where basis is sufficient, the at-risk rules and passive activity rules can still suspend losses.