Mileage Logs: What Actually Has to Be In One

Vehicle expenses are among the most commonly claimed deductions for self-employed people and small business owners, and they carry substantiation requirements stricter than most other categories. A deduction that is entirely legitimate can be disallowed purely because the records supporting it are not adequate.

Why vehicles get stricter treatment

A vehicle is used for both business and personal purposes in almost every case. That mixed-use character is exactly why the documentation standard is higher — the records have to establish not just that you spent money on a vehicle, but what portion of its use was business.

Without a log, there is no basis on which to allocate. That is the core problem.

What a log needs to contain

For each business trip, the record should establish:

• The date
• The destination
• The business purpose — who you met, what you delivered, what the trip accomplished
• The miles driven for that trip

Alongside the trip records, you want the vehicle's total mileage for the year, which is what lets you establish the business-use percentage. Odometer readings at the start and end of the year handle that.

Contemporaneous matters here more than anywhere

The expectation for vehicle records is that they were made at or near the time of the travel. A log kept as you drive — an app entry, a note in a notebook in the console — is materially stronger than a spreadsheet assembled in March from calendar entries and memory.

Reconstructions are not automatically worthless, and they are weaker, and they take considerably more effort than just keeping the log would have. The reconstruction also tends to be less accurate, which usually means claiming less than you were actually entitled to.

The two methods, and why your records differ

The standard mileage rate multiplies business miles by a per-mile rate set by the IRS, which is adjusted periodically. This method requires a solid mileage log and relatively little else. Note that the rate changes and you should confirm the current figure for the tax year rather than relying on a number you remember.

Actual expenses means tracking the real costs of operating the vehicle — fuel, insurance, repairs, depreciation and so on — and deducting the business-use percentage of them. This method requires the mileage log plus receipts for every expense.

Either way, you need the log. The choice between methods has other implications, including rules about switching between them in later years, which is worth discussing before you commit in the first year a vehicle is placed in service.

What counts as business mileage

This is where people make honest mistakes in both directions. Commuting between your home and a regular place of business is generally personal, not deductible — that surprises people. Travel between business locations, to client meetings, to pick up supplies, or to a temporary work location is generally business.

The home office situation changes the analysis in ways worth understanding, because if your home is your principal place of business, trips from there to other business locations may be treated differently than an ordinary commute.

These distinctions have real substance to them, and getting them wrong in either direction costs you — either in disallowed deductions or in deductions you were entitled to and never claimed.

Apps make this genuinely easy

Mileage tracking apps that use your phone's location to log trips automatically have made this a solved problem. They capture the date, the route and the mileage, and they let you categorize each trip as business or personal, usually with a note field for purpose.

The categorization step is the part that still requires you. An app that logs every trip and has none of them categorized has captured data, not a record.

The practical advice

Pick a method — app or notebook — and use it every time, from the first business trip of the year. Record purpose along with mileage, because the purpose is the part reconstructions cannot recover. Capture the odometer at the start and end of the year.

That routine takes seconds per trip and it converts a vulnerable deduction into a well-supported one.

RD Precision Tax Service works with self-employed people and small business owners across Weatherford and Parker County on exactly this kind of documentation.