To be deductible, a business expense has to be both ordinary and necessary. Those are not loose adjectives — they are the legal test, and each has a specific meaning. An ordinary expense is one that is common and accepted in your trade or business. A necessary expense is one that is helpful and appropriate for it.
Notice what necessary does not mean: it does not mean indispensable. An expense can be genuinely useful without being something you could not survive without.
The line that matters most
Personal, living and family expenses are generally not deductible. Nearly every real dispute about a business deduction is a dispute about which side of that line something falls on, not about whether the category exists.
The hard cases are the mixed ones — the phone used for both, the car that does both, the trip that was mostly business. Mixed-use items are not automatically disallowed, but they are the items where documentation stops being paperwork and becomes the whole argument.
Two numbers worth knowing
- Mileage. The standard mileage rate for business use is 72.5 cents per mile for 2026, up 2.5 cents from the prior year. It is an alternative to tracking actual vehicle costs, and either way it requires a record of the miles.
- Meals. You may generally deduct 50% of the cost of a business meal, provided you or an employee is present and the food is not lavish or extravagant. The meal can be with a current or potential customer, client, consultant or similar business contact.
For equipment purchases, Section 179 lets a business elect to expense the cost rather than depreciate it over years. For tax years beginning in 2025 the aggregate limit is $2,500,000, with a separate cap of $31,300 on the amount that can be taken for a sport utility vehicle. Confirm the current year's figures before relying on them — these are adjusted regularly.
The part that actually decides an audit
You generally must have documentary evidence — receipts, canceled checks or bills — to support your expenses. If the IRS examines your return, you will be asked to explain the items you reported.
That is the whole game, and it is worth being blunt about it: an expense you cannot substantiate is not a deduction you took, it is a deduction you are hoping to keep. A bank statement showing $400 at a supplier proves you spent $400. It does not prove what you bought or why the business needed it.
The IRS does not prescribe a particular system. You may choose any recordkeeping system suited to your business that clearly shows income and expenses — it can be as simple as a calendar with the day's income and expenses, or as involved as a full accounting package. What it cannot be is absent, or reconstructed in April from memory.
The home office, and the easy way to claim it
If part of your home qualifies for business use, there is a simplified method that avoids allocating your actual household costs. The prescribed rate is $5.00 per square foot, the allowable area is the lesser of the space used or 300 square feet, and the maximum deduction under this method is therefore $1,500.
The trade-off is real: using the simplified method, you cannot also deduct depreciation — including additional first-year depreciation — or a Section 179 expense for that portion of the home in the same year. For a small space the simplified method usually wins on effort. For a large one it can leave money behind, and it is worth calculating both ways once rather than assuming.
How long to keep the records
Keep records supporting income, deductions and credits until the period of limitations for that return runs out — generally three years, with several situations extending it. Records that establish basis in property are the exception worth flagging: keep purchase documents for equipment, vehicles and real property for as long as you own the asset, plus the limitations period after you sell it.
Why this argues for monthly, not annual, bookkeeping
A record made at the time is evidence. A record made eleven months later is a recollection. The practical difference shows up in exactly the mixed-use cases above, where the question is not what you spent but what it was for — and nobody remembers the purpose of a Tuesday lunch the following March.
This is the honest argument for keeping books as you go rather than in a rush: not that it is tidier, but that it is the only version that survives being questioned. That is what monthly bookkeeping and accounting is for, and it feeds directly into corporate tax preparation at year end instead of starting from a box.
Where to be careful
Self-employed filers report business expenses on Schedule C of Form 1040, or Schedule F for farming. Beyond the mechanics, the categories that draw the most scrutiny are the ones that most resemble personal spending: vehicles, meals, travel, home office, and anything involving family members on payroll. None of them are off limits. All of them need a record that says what the business purpose was.
Figures above are the years stated and reflect IRS guidance current as of July 2026. This is general information, not advice about your business's deductions.
If your books are behind, fix that before you file
Bring your bank and credit card statements, whatever mileage record you have, and your payroll reports if you have employees. We will tell you what is substantiated, what is not, and what to start capturing now so next year does not require the same excavation. Start with monthly bookkeeping, or call +1 (954) 724-1114.