What to write as the business purpose of a drive
A log with dates and miles but no reasons is half a log. Where the IRS asks for a purpose, the one narrow exception, and what a purpose line that holds up looks like.
Most mileage logs get the easy parts right. The date is there, the miles are there, often the destination too. The column that stays empty is the one that says why the drive was business — and it is the one the rules name outright.
This piece is about that column: where the requirement comes from, when the IRS lets it go, and what to actually write.
Where the rule is written
It starts in the tax code. Section 274(d) says that no deduction is allowed for “listed property” — which includes your car — unless you substantiate, among other things, “the business purpose of the expense or other item.” The wording is not “should” or “where possible”. Without substantiation there is no deduction.
Publication 463, the IRS’s guide to car and travel expenses, turns that into a checklist. Its Table 5-1, How To Prove Certain Business Expenses, lists what a car record has to show:
| Element | What the IRS lists for car expenses |
|---|---|
| Amount | The mileage for each business use, and the total miles for the year |
| Time | The date of the use of the car |
| Place | Your business destination |
| Business purpose | Business purpose for the expense |
And the text around it is direct: “You must generally provide a written statement of the business purpose of an expense.”
The exception is narrower than it sounds
The same paragraph goes on: “If the business purpose of an expense is clear from the surrounding circumstances, then you don’t need to give a written explanation.”
It is easy to read that as permission to skip the column. The example the IRS gives shows how narrow it is: “If you are a sales representative who calls on customers on an established sales route, you don’t have to give a written explanation of the business purpose for traveling that route.”
That works because the route itself is the explanation — the same drive, for the same reason, over and over. A drive to a supplier on Tuesday, a client on Wednesday and the bank on Thursday has no such pattern. Nothing about the destination alone says why you went, and whether it is “clear from the surrounding circumstances” is decided by the person examining your return, not by you.
If you have to wonder whether the exception covers you, write the purpose.
“Business” is not a purpose
A category says the drive was business. A purpose says why. Marking a drive Business and leaving it there answers a question the IRS did not ask.
| Too thin | Holds up |
|---|---|
| Business | Site visit — Hendricks kitchen remodel |
| Meeting | Quarterly review with Pine Street Dental |
| Work | Showing 412 Oak St to the Marsh family |
| Errand | Materials for the Hendricks job — Lowe’s |
| Client | Delivered signed contract to Crestview HOA |
The pattern is simple: what you did, and for whom — a client, a job, a property. One line is enough. Nobody expects a paragraph.
Purpose lines by trade
| If you are a… | A purpose line might read |
|---|---|
| Real estate agent | Listing appointment — 88 Birch Ln (Walker) |
| Contractor | Inspection at the Garza bathroom job |
| Consultant | Onsite workshop at Tri-County Credit Union |
| Photographer | Wedding shoot — Harlow/Kim, Sycamore Barn |
| Home care nurse | Visit to patient, Elm St route (weekly) |
| Rideshare or delivery driver | Online for DoorDash — deliveries |
For gig work the app’s own trip history already says what each drive was, so the purpose can be short. It still belongs in the log: the log is what you hand over, not a login to someone else’s app.
When to write it
The IRS does not ask you to write every detail the moment you park. Publication 463, chapter 5 says a record made “at or near the time” is what counts, and spells out what that means in practice: “If you maintain a log on a weekly basis that accounts for use during the week, the log is considered a timely kept record.”
So a weekly habit is enough. Ten minutes on Friday, while the week is still fresh, is a timely record. The same ten minutes the following April, reconstructing the year from memory and a calendar, is a much weaker one.
Habits that make it painless
- Name the client or the job, not just the activity. “Meeting” is forgettable by March; “Pine Street Dental” is not.
- Reuse wording for drives you repeat. The same client, the same reason, the same line. It reads as a pattern because it is one.
- A round trip is one use. Publication 463 allows “several uses of your car that can be considered part of a single use, such as a round trip or uninterrupted business use” to be recorded as one, so the drive out and the drive back share a purpose.
- Let the purpose point at something else you keep — an invoice, a calendar entry, a receipt. The statute asks for adequate records or evidence that corroborates your own statement; a purpose that matches your invoices does both.
A purpose line that holds up
- says why the drive was business, not just that it was
- names the client, job, or place it was for
- is written the same week as the drive
- matches something else you keep: an invoice, a calendar, a receipt
Where odo fits
odo records the date, the route and the miles on its own. The purpose is the one thing a phone cannot know, so it is a line you add to the drive — and a drive you make often can carry its purpose in its rule, so it fills in by itself. When you make a report, any business drive without a purpose is marked Not recorded, so you can fix it while you still remember.
The free plan covers 35 drives a month, and Pro removes the limit.
The bottom line
Dates and miles show that you drove. The purpose shows why it was deductible. The rule asks for it on every business drive, the exception covers only drives whose reason is obvious from the pattern, and one specific line written the same week is all it takes.
Sources
- IRS, Publication 463: Travel, Gift, and Car Expenses — chapter 5, Recordkeeping: Table 5-1, Proving business purpose, Timely kept records, Separating and Combining Expenses.
- 26 U.S. Code § 274(d) — substantiation required for listed property, including business purpose.
- 26 CFR § 1.274-5T — the regulation behind it: the elements to prove, and what counts as an adequate record.
This article is general information, not tax advice. Tax situations vary — check with a qualified professional before you file.