Whether you drive to client offices, job sites, rental properties or the supply store, your mileage log has to tell the story of each business trip. That matters even more in 2026 because miles through June 30 use 72.5¢ per mile and miles beginning July 1 use 76¢.

The four fields to record for every business trip

1. Date When the vehicle was used

The trip date identifies the correct 2026 rate period and satisfies the time element of the substantiation rule.

2. Business miles How far you drove

Record the mileage for the trip and maintain total annual mileage so business use can be distinguished from commuting and other personal use.

3. Destination Where the trip went

Identify the destination or locality with enough detail to connect the travel to the activity claimed.

4. Business purpose Why the trip was necessary

Use a specific explanation—such as “meet client about project” or “pick up business supplies”—rather than a vague label such as “business.”

The rules allow the level of detail to vary with the facts. For example, an established delivery route may be documented differently from irregular client visits. The core elements still must be established.

“At or near the time” does not mean once at year-end

An adequate record may be an account book, diary, mileage app, log, trip sheet or similar record, supported where appropriate by other documents. The regulation gives greater weight to records prepared when the taxpayer still has full present knowledge of the trip.

The standard mileage rate proves only part of the claim

Multiplying miles by an IRS rate computes the dollar amount. It does not prove that the miles were driven for business. The taxpayer must still establish the amount of each business use, when it occurred and its business purpose.

That is why an odometer reading on January 1 and December 31 is not, by itself, a complete business-mileage log. It may help establish total annual miles, but it does not identify individual business trips—or split the 2026 miles at July 1.

For a plain-language explanation of the two rates and a calculation example, read 2026 Business Mileage Rates Changed Midyear.

What if the log is incomplete?

Section 274(d) uses strict substantiation rules for vehicle use. Unsupported estimates or a generalized statement that a percentage of driving was “for business” are not a dependable substitute for the required evidence.

If adequate records are incomplete, the regulation allows other sufficient evidence in limited circumstances. The taxpayer must provide a detailed statement and corroborating evidence. Direct evidence is required for elements such as mileage, cost, date or place; circumstantial evidence may be considered for business purpose.

Sampling is allowed only when it is genuinely representative

The regulation permits records from a representative portion of the year to support business use for a larger period when other evidence demonstrates that the recorded period accurately represents the unrecorded period. This is not permission to pick the busiest week or assume every month was the same.

For example, the regulation describes a business with three months of adequate records showing 75% business use, supported by invoices showing the business continued at approximately the same rate for the rest of the year. By contrast, a salesperson’s delivery-heavy week was not representative of weeks with irregular driving.

What if records were destroyed?

When records are lost because of circumstances beyond the taxpayer’s control—such as fire, flood, earthquake or another casualty—the regulation permits reasonable reconstruction. That relief is tied to an actual loss beyond the taxpayer’s control; it is not the same as never having kept records.

A practical 2026 mileage-log template

For each trip, use columns for:

At year-end, total business miles separately for January 1–June 30 and July 1–December 31. Also retain the information needed to report total, business, commuting and other personal mileage and to calculate the business-use percentage.

Official sources

General information only. This article is not legal or individualized tax advice. Whether a record satisfies the substantiation rules depends on all the facts and supporting evidence.

Facing an audit or rebuilding missing records?

If the log is incomplete, no panic—but no make guesses either. Kōkua Tax helps Hawaiʻi taxpayers organize the available evidence, understand what the IRS is requesting and respond with a clear strategy.

Talk with a local tax professional