What the IRS Actually Requires
Revenue Procedure 2010-51 and Treasury Regulation §1.274-5 set the standard: ‘adequate records’ means an account book, diary, log, statement of expense, trip sheets, or similar record made at or near the time of the expenditure. The record must show: (1) the date of the trip, (2) the destination or route, (3) the business purpose, and (4) the number of miles driven.
Critically, the IRS expects ‘contemporaneous’ records — meaning created at or near the time of the business use. A spreadsheet you populate in March 2027 to reconstruct your 2026 mileage does not meet the standard, and auditors are specifically trained to identify retrospective logs.
Required Elements of a Compliant Mileage Log
| Field | Example | Why It Matters |
|---|---|---|
| Date | 2026-05-15 | Establishes which tax year the trip belongs to |
| Starting odometer | 45,230 | Shows beginning of trip (or day) |
| Ending odometer | 45,312 | Proves total miles traveled |
| Destination | Client office, 123 Main St, Chicago | Confirms business location |
| Purpose | Quarterly review meeting with Acme Corp | Establishes business nexus |
| Total miles | 82 | Quick reference for calculation |
Example of a single-trip entry.
Digital vs Paper: What Auditors Look For
Digital mileage tracking apps (MileIQ, Everlance, TripLog, etc.) are accepted by the IRS and have the advantage of automatic GPS tracking and timestamped records. However, IRS auditors look for: (1) trips that appear to be personal but are classified as business, (2) round numbers that suggest estimation rather than measurement, and (3) gaps in the log that suggest missing trips.
Paper logs are equally valid but easier to challenge — auditors may question whether a paper log was truly contemporaneous if all entries are in the same pen and handwriting with no signs of daily variation.
Regardless of format, the best practice is to record each trip on the same day it occurs. Set a daily reminder. For frequent short trips, a running daily log with aggregate miles per purpose is acceptable.
Common Audit Triggers
IRS mileage audits most commonly target: (1) large round-number mileage claims (10,000, 15,000, 20,000 exactly), (2) Schedule C filers claiming 100% business use of a vehicle, (3) years where the taxpayer switched between standard rate and actual expenses, and (4) claims that are disproportionate to the taxpayer’s reported income.
If you drive 30,000 miles for a side business generating $5,000 in revenue, expect questions. The IRS understands that some businesses are vehicle-intensive (rideshare, delivery), but the mileage-to-revenue ratio should be reasonable.