Most missed deductions are not exotic. They are ordinary business costs that were never recorded, or were recorded without the documentation needed to defend them. Here are the categories we recover most often when we take over a set of books, and what proper substantiation looks like for each.
The home office deduction, claimed correctly
A space used regularly and exclusively for business can support a deduction based on the square footage it occupies. Owners skip it either because they assume it invites scrutiny or because they never measured the room. Neither is a good reason to give up a legitimate deduction.
Keep the measurement, a simple floor-plan note, and copies of the household bills you are allocating. That file takes an hour to build once and supports the deduction every year afterward.
Mileage and vehicle costs
Business mileage is one of the largest deductions available to service businesses, and the one most often reconstructed from memory in April. A contemporaneous log — date, destination, purpose, miles — is what makes the number defensible.
You may deduct either the standard mileage rate or actual costs, but the choice interacts with depreciation and how the vehicle was first placed in service. Decide deliberately rather than by default.
- Log trips as they happen, not at year-end
- Record purpose, not just distance
- Keep commuting miles separate — they are not deductible
Equipment, software, and startup costs
Computers, tools, furniture, and software often qualify for immediate expensing rather than multi-year depreciation, which can dramatically change your current-year liability. Costs incurred before the business opened may also be deductible or amortizable.
The mistake we see is not aggressive deduction — it is quiet omission, where a purchase paid from a personal card never enters the business records at all.
Professional fees, insurance, and retirement
Accounting, legal, and consulting fees are deductible business expenses, as are business insurance premiums and, in many cases, self-employed health insurance. Retirement contributions through a SEP or solo plan remain one of the most effective ways to lower taxable income while building personal assets.
These are planning decisions, which means they have to be made before the year closes. Reviewing them in the fourth quarter is far more valuable than discussing them at filing time.
Documentation is the deduction
A deduction you cannot substantiate is a deduction you may lose in an examination. Separate business and personal accounts, capture receipts digitally as they occur, and note business purpose on anything that could look personal.
Clean monthly books make this automatic. That is why bookkeeping and tax strategy work best together rather than as separate annual events.
Key takeaway
Record every business cost as it happens, keep purpose-level documentation, and revisit equipment and retirement decisions in the fourth quarter while you can still act on them.
