Tax
Business Deductions and Records That Hold Up Under Scrutiny
Two errors cost owners money in roughly equal measure: claiming things that were never deductible, and failing to claim things that were, because the records were not there to support them.
Key points
- The standard is ordinary and necessary — common in your trade, and helpful for the business. Not “I bought it with the business card”.
- A deduction reduces taxable income, not tax. Spending a dollar to save a fraction of a dollar is still spending.
- The home office deduction is legitimate and widely under-claimed, but demands exclusive and regular business use.
- Vehicle and travel claims are audited more than most, and both require contemporaneous records rather than a year-end reconstruction.
- Records must be retained for years after filing — the deduction is only as good as the evidence behind it.
The test every deduction has to pass
US tax law allows a deduction for expenses that are ordinary and necessary in carrying on a trade or business. Both words carry weight:
- Ordinary — common and accepted in your line of work. Not unheard of for a business like yours.
- Necessary — helpful and appropriate for the business. It does not have to be indispensable, but it must serve a genuine business purpose.
The expense must also be reasonable in amount and genuinely business-related. Where something serves both business and personal purposes, only the business portion is deductible, and you need a defensible basis for the split.
A deduction reduces taxable income, not tax owed. If your combined marginal rate is 30%, a $1,000 deductible purchase saves $300 — and costs you $1,000. Buying things you do not need in December “for the write-off” leaves you poorer, not richer. Deductions are worth claiming on money you were going to spend anyway.
What ordinary businesses actually deduct
The categories below cover most of what a typical small business claims:
- Rent for business premises, and utilities for that space
- Wages and contractor payments, plus the employer share of payroll taxes
- Supplies and materials consumed in the business
- Software subscriptions, hosting, domains, professional tools
- Professional fees — accounting, legal, consulting
- Business insurance premiums
- Marketing and advertising, including agency and platform spend
- Bank and merchant processing fees
- Interest on business borrowing, subject to limitation rules for larger businesses
- Training and education that maintains or improves skills used in your current business — not education qualifying you for a new trade
- Business travel, and meals subject to their own percentage limit
- Equipment, either depreciated or expensed under the rules below
Two categories worth calling out because owners routinely get them wrong:
Meals and entertainment. Business meals are generally deductible at a limited percentage, while entertainment expenses were largely eliminated as deductions by the Tax Cuts and Jobs Act. The applicable percentages have changed several times in recent years, including temporary provisions, so confirm the current position [VERIFY: current deductible percentage for business meals, and the entertainment position, irs.gov Publication 463].
Startup costs. Expenses incurred before the business opened are treated under separate rules — a limited amount may be deducted immediately with the balance amortised over a period of years, subject to phase-out thresholds [VERIFY: current startup and organisational cost deduction limits, phase-out threshold and amortisation period, irs.gov].
The home office deduction, done properly
This deduction is legitimate, frequently under-claimed out of unfounded audit anxiety, and genuinely valuable to anyone running a business from home. It also has a strict entry condition.
Exclusive and regular use
The space must be used exclusively and regularly for business, and must generally be your principal place of business. Exclusive is the word that disqualifies most claims: a dining table that becomes a desk on weekdays does not qualify. A spare room used only for work does. The space does not need to be an entire room, but it must be identifiable and not used for personal purposes.
Two ways to calculate it
The simplified method applies a fixed rate per square foot up to a capped area — no receipts for household bills, minimal record-keeping [VERIFY: current simplified-method rate per square foot and maximum allowable square footage, irs.gov Publication 587].
The actual expense method takes the business-use percentage of your home (typically office square footage divided by total) and applies it to mortgage interest or rent, property tax, utilities, insurance, repairs and depreciation. More work, and usually a larger deduction.
You can choose method by year. Run both once and see which produces more; if the actual method wins substantially, the extra bookkeeping is worth it.
If you use the actual method and depreciate part of your home, that depreciation may be subject to recapture when you sell, affecting the gain calculation. It does not necessarily make the deduction a bad idea, but discuss it with your accountant rather than discovering it at closing.
Vehicle expenses and the record that makes them stick
You may deduct the cost of business use of a vehicle by one of two methods.
Standard mileage. Multiply business miles by the IRS standard rate, which is set annually [VERIFY: current-year IRS standard mileage rate for business use, irs.gov]. Simple, and it covers fuel, maintenance, insurance and depreciation collectively. Parking and tolls are claimed separately.
Actual expenses. Total your real costs — fuel, insurance, repairs, registration, depreciation or lease payments — and deduct the business-use percentage.
There are restrictions on switching between methods for a given vehicle, particularly where depreciation methods have been used, so the first-year choice matters.
Commuting is not business mileage
Travel between home and your regular place of business is a personal commute and is not deductible. Travel between business locations, to clients, or to suppliers generally is. Where a qualifying home office is your principal place of business, trips from there to other work locations may count — one of the quieter benefits of the home office deduction.
The log is the deduction
Whichever method you use, you need a contemporaneous record of business mileage: date, destination, purpose and miles. “Contemporaneous” means kept as you go, not reconstructed in April from calendar entries. Vehicle deductions are examined often, and a reconstructed estimate is the weakest possible position. Any of the mileage-tracking apps will do this automatically from your phone.
Equipment: expense it now or depreciate it
Buy something with a useful life beyond a year — a machine, a vehicle, computers, furniture — and the default treatment is depreciation, deducting the cost over a period of years. Two provisions let you accelerate that:
- Section 179 expensing lets you deduct the full cost of qualifying property in the year it is placed in service, up to an annual dollar limit, with a phase-out once total purchases exceed a threshold. It is also limited by business income.
- Bonus depreciation allows an additional first-year deduction on qualifying property. The applicable percentage has been subject to a legislated phase-down schedule and to subsequent legislative change.
Both sets of figures move, and the bonus depreciation percentage in particular has changed repeatedly. Confirm the current position before planning a purchase around it [VERIFY: current Section 179 deduction limit and phase-out threshold, and current bonus depreciation percentage, irs.gov].
There are also specific limitations on certain vehicles, and rules about property placed in service late in the year. Large equipment decisions are worth a conversation with your accountant before the purchase, not after — timing across a year end can change the outcome materially.
What substantiation actually means
A deduction you cannot evidence is a deduction you may lose. For most expenses you need to be able to show what was bought, when, how much it cost, and why it was a business expense.
Practically, keep:
- Receipts and invoices — photographed or scanned is fine, and more durable than thermal paper
- Bank and credit card statements for the business accounts
- Mileage logs with date, destination, purpose, distance
- A note of business purpose for meals and travel — who, and why
- Contracts and agreements for significant commitments
- Payroll records and contractor documentation, including W-9s and 1099s issued
- Asset records — purchase date, cost and depreciation schedule for each capitalised item
How long to keep it
Retention periods depend on the situation. The general period for assessment runs a set number of years from filing, extends where income has been substantially understated, and does not begin at all where no return was filed or where fraud is involved. Employment tax records and records supporting the basis of assets you still own have their own, longer requirements — asset records in particular should be kept until well after that asset is disposed of [VERIFY: current IRS record retention periods by situation, irs.gov 'How long should I keep records?'].
Storage is cheap. When in doubt, keep it.
The errors that cost the most
Mixing personal and business spending. This is the root cause of most other problems. It makes bookkeeping expensive, weakens your liability protection, and turns any examination into a line-by-line argument. One business account and one business card solves it.
Claiming full deduction on mixed-use items. A phone, a laptop or a vehicle used for both purposes is deductible only to the extent of business use, and you need a reasonable basis for the percentage you claim.
Reconstructing records after the fact. Contemporaneous documentation carries weight; a spreadsheet built in April from memory does not.
Deducting things that are simply not deductible. Political contributions, most fines and penalties, personal clothing that is suitable for ordinary wear even if you only wear it for work, and personal living expenses do not qualify regardless of how the payment was made.
Buying to save tax. Worth repeating because it is expensive: a deduction returns only your marginal rate. If you did not need the equipment, the purchase made you poorer.
Missing deductions entirely. The most common omissions are the home office, mileage, a portion of phone and internet, professional development, and bank fees. These are real deductions that owners forgo because tracking felt like too much effort.
Set the systems up once — separate accounts, an automatic mileage tracker, a receipt-capture app, monthly reconciliation — and both problems largely solve themselves.
Educational information only. This guide explains how US business finance generally works. It is not financial, tax, investment or legal advice, and it does not account for your circumstances. Tax figures change annually and rules vary by state — anything highlighted for verification must be confirmed against current IRS or state guidance. Consult a qualified professional before acting. See the full disclaimer.