How to Create an IRS-Proof Mileage Log
The Complete 2026 Guide to Publication 463, IRC §274(d), and Audit-Proof Record-Keeping
Vehicle expenses are one of the most commonly audited deductions on Schedule C. The reason is simple: the IRS knows from decades of experience that many taxpayers exaggerate their business mileage or, more often, simply fail to keep the records required by law.
If you claim a mileage deduction and are selected for an audit, the IRS agent will ask for one thing first: your mileage log. Not a rough estimate. Not a calendar with appointments circled. A detailed, contemporaneous record that satisfies the requirements of IRS Publication 463 and Internal Revenue Code §274(d).
This guide explains exactly what those requirements are, why they exist, the different ways to keep compliant records, and what happens when you fall short. Whether you are a real estate agent, a gig worker, a contractor, or any self-employed professional who drives for business, this is the article you need to read before your next tax filing.
1. Why the IRS Scrutinizes Vehicle Deductions
The IRS has identified vehicle expense deductions as a high-risk area for non-compliance for many years. Schedule C filers who claim vehicle expenses are audited at significantly higher rates than those who do not. There are several reasons for this:
- Nearly every vehicle has personal use. Unlike a piece of office equipment that sits in your workplace, your car goes everywhere — grocery stores, soccer practice, and vacation. The IRS knows that separating business from personal use requires discipline, and most people lack it.
- The deduction is large. At the 2026 standard mileage rate of 72.5 cents per mile, a taxpayer claiming 20,000 business miles is deducting $14,500. That is real money, and it is worth the IRS's time to verify.
- Documentation failures are common. The IRS has found through audits that a significant percentage of taxpayers who claim mileage deductions either have no log at all or have logs that were clearly created after the fact.
- Vehicles are "listed property." Under IRC §280F, passenger automobiles are classified as "listed property," which subjects them to stricter substantiation requirements than ordinary business expenses. The IRS applies the heightened standards of §274(d) to all vehicle deductions.
The bottom line: if you drive for business and claim a deduction, the quality of your mileage log is your single most important piece of documentation.
2. What “Contemporaneous” Means Legally
The Most Common Reason Mileage Deductions Are Denied
The word “contemporaneous” appears throughout IRS guidance on record-keeping for vehicle expenses. It means recorded at or near the time of the expense. The IRS does not require you to log every trip the instant you park your car, but it expects entries to be made while the details are fresh — ideally the same day, or at minimum the same week.
Treasury Regulation §1.274-5T(c)(1) provides that a taxpayer must maintain an “adequate record” or have “sufficient evidence corroborating the taxpayer's own statement” to substantiate each element of a vehicle expense. The regulation specifically states that a record made at or near the time of the expenditure has “more probative value than a statement prepared subsequently.”
In practical terms, this means:
- A mileage log created in April 2027 for the 2026 tax year is not contemporaneous and will almost certainly be rejected in an audit.
- A spreadsheet with file metadata showing all entries were created on a single date is a red flag for auditors.
- GPS-timestamped records from a mileage tracking app are inherently contemporaneous because each trip is recorded in real time with a timestamp that is virtually impossible to alter retroactively.
The IRS does not need to prove that your log is fabricated. The burden of proof is on you, the taxpayer, to demonstrate that your records were maintained contemporaneously. If your records do not clearly show when they were created, the IRS can — and routinely does — disallow the entire deduction.
3. The 5 Required Data Points (Per IRS Publication 463)
IRS Publication 463, “Travel, Gift, and Car Expenses,” specifies that for each business trip, your records must include the following five elements. Missing even one can give an auditor grounds to challenge the entry.
1. Date of the Trip
The month, day, and year of each business drive. A vague entry like 'January' is not sufficient — you need the specific date.
2. Mileage Driven
The total miles driven for that specific trip. This should be the distance from your starting point to the destination and back, or to the next business stop.
3. Destination
Where did you drive? Record the city or town and the street address, or the name of the business or client you visited.
4. Business Purpose
Why did you make the trip? Entries like 'Client meeting with ABC Corp' or 'Property showing at 123 Oak St' are specific enough. 'Business' alone is not.
5. Odometer Readings
Record your total odometer reading at the start and end of the tax year. This lets the IRS verify your claimed business percentage against total miles driven.
Note on odometer readings: Unlike the first four data points (which are per-trip), the odometer reading requirement is annual. Record your total odometer at the start and end of each tax year (January 1 and December 31). The IRS uses these totals to verify that your claimed business miles, plus your personal miles, add up to a reasonable total.
4. What Constitutes “Adequate Records”
IRC §274(d) states that no deduction shall be allowed for listed property (including vehicles) unless the taxpayer substantiates the expense with “adequate records” or “sufficient evidence corroborating the taxpayer's own statement.” IRS Publication 463 elaborates on what “adequate records” means in practice:
An account book, diary, log, trip sheet, or similar record that is kept at or near the time of each trip and records each of the five required elements.
Documentary evidence such as receipts or GPS-generated reports that corroborate the mileage, date, and destination.
Records that together are sufficient to establish each element. For example, a GPS log that captures date, route, and mileage combined with a separate note of the business purpose constitutes adequate records.
Publication 463 explicitly notes that you do not need to record information that is already available in your account book or other records. For example, if you use a GPS-based mileage tracker that automatically captures date, distance, and route, you only need to manually add the business purpose for each trip. This is one reason why automatic tracking apps have become the preferred method for maintaining IRS-compliant records.
5. Paper Log vs. Spreadsheet vs. App
The IRS does not mandate a specific format for your mileage log. A paper notebook is just as legally valid as a sophisticated app — as long as it contains the five required elements and is kept contemporaneously. However, each method has significant practical differences that affect your ability to stay compliant:
Paper Log / Notebook
Pros
- No cost — any notebook works
- No technology required
- Simple and immediately understandable to an auditor
Cons
- Easy to forget to fill out after a busy day
- Not contemporaneous if entries are batched at the end of the week
- Can be lost, damaged, or illegible
- No automatic backup
Bottom line: Acceptable if you are extremely disciplined, but most people fall behind within weeks.
Spreadsheet (Excel / Google Sheets)
Pros
- Free or low-cost
- Easy to organize and total up at year-end
- Can calculate deduction value automatically
- Digital file is harder to lose than paper
Cons
- Easy to backdate entries (auditors know this)
- File metadata can reveal when entries were actually created
- Still requires manual data entry after every trip
- No GPS verification of routes or distances
Bottom line: Better than paper, but the IRS knows spreadsheets are easy to fabricate.
Automatic Mileage Tracking App
Pros
- GPS captures date, distance, and route automatically
- Entries are timestamped and near-impossible to backdate
- Digital audit trail that is inherently contemporaneous
- IRS-compliant reports generated with one click
- Captures trips you would have forgotten to log manually
Cons
- May have a subscription fee (though many offer free tiers)
- Requires a smartphone with GPS enabled
- You still need to classify the business purpose of each trip
Bottom line: The gold standard. Apps like tiktraq create the kind of timestamped, GPS-verified records that are hardest for an auditor to challenge.
6. What Happens During a Mileage Audit
If the IRS selects your return for examination and you have claimed a vehicle expense deduction, here is what typically happens:
The IRS requests your records
You will receive a letter (usually Letter 566 or Letter 525) requesting documentation to support your claimed vehicle expenses. You generally have 30 days to respond.
The examiner reviews your mileage log
The agent looks for the five required data points for each trip. They will check whether entries appear to be made contemporaneously or if they were clearly created in bulk. They may also examine digital file metadata on spreadsheets.
Cross-referencing with other records
The agent may compare your mileage log against your calendar, appointment records, client lists, and even Google Maps to verify that the distances you claimed are plausible for the routes described.
The odometer sanity check
Using your beginning-of-year and end-of-year odometer readings, the agent calculates total miles driven. They then check whether your claimed business miles, plus a reasonable estimate of personal miles, add up to the total. If you claim 25,000 business miles but your total annual mileage was only 28,000, you are claiming that 89% of your driving was for business — a figure that will draw scrutiny unless you can justify it.
The outcome
If your records are adequate, the deduction stands. If your records are incomplete, the agent will either reduce or completely disallow the deduction. You will owe additional tax, plus interest, and potentially accuracy-related penalties of 20% under IRC §6662.
7. The Cohan Rule — Can You Estimate?
Some taxpayers believe they can simply estimate their mileage and rely on the so-called “Cohan Rule” to salvage a deduction. Here is why that is a dangerous strategy for vehicle expenses:
The Cohan Rule comes from Cohan v. Commissioner, 39 F.2d 540 (2d Cir. 1930), in which the Second Circuit Court of Appeals held that where a taxpayer has established that deductible expenses were incurred but cannot prove the exact amount, the court may estimate a reasonable deduction rather than disallow it entirely.
Critical Limitation: §274(d) Overrides the Cohan Rule
In 1962, Congress enacted IRC §274(d) specifically to impose strict substantiation requirements on travel, entertainment, gifts, and listed property (including vehicles). The legislative intent was clear: these are the exact categories of expenses that are most prone to abuse, and the Cohan Rule's tolerance for estimates was not sufficient.
The IRS's position — consistently upheld by the Tax Court — is that the Cohan Rule does not apply to expenses subject to the strict substantiation requirements of §274(d). If you have no adequate records for your vehicle expenses, the IRS can disallow the entire deduction, not just a portion.
In some cases, the Tax Court has allowed partial deductions where the taxpayer could produce some corroborating evidence (such as a calendar or testimony), but these outcomes are unpredictable and should never be relied on as a strategy. The safest course of action is always to maintain adequate, contemporaneous records.
8. Mixed-Use Vehicles: Calculating Your Business Percentage
Most self-employed individuals use the same vehicle for both business and personal driving. The IRS requires you to determine and document your “business-use percentage” each year. Here is how it works:
The Formula
Business-Use % = (Business Miles ÷ Total Miles) × 100
Example: You drive 30,000 total miles in 2026. Of those, 18,000 are documented business miles and 12,000 are personal. Your business-use percentage is 60%.
- Standard mileage rate: You deduct 18,000 × $0.725 = $13,050 directly. No separate business-percentage calculation is needed because you are only counting business miles.
- Actual expense method: You deduct 60% of all vehicle-related expenses (gas, insurance, repairs, depreciation, etc.). This requires keeping receipts for every vehicle cost in addition to your mileage log.
In either case, the odometer readings are essential. They allow the IRS to verify your total annual mileage, which in turn validates your business percentage. If you cannot produce beginning-of-year and end-of-year odometer readings, an auditor may use vehicle maintenance records (such as oil change stickers) to independently estimate your total mileage — and if their estimate produces a lower business percentage than you claimed, your deduction will be reduced. Watch out for related pitfalls in our guide on common tax mistakes real estate agents make.
9. Record Retention: How Long to Keep Your Mileage Logs
Creating a great mileage log is only half the battle. You also need to keep it for the required retention period. Here are the IRS rules:
The general rule. The IRS generally has three years from the date you filed your return (or the due date, whichever is later) to audit you. This is the standard statute of limitations under IRC §6501(a).
Substantial understatement. If the IRS determines that you omitted more than 25% of your gross income from your return, the statute of limitations extends to six years under IRC §6501(e).
Fraud or no return filed: There is no statute of limitations. The IRS can audit you at any time. Keep your records indefinitely if there is any question about whether a return was filed.
Our recommendation: Keep your mileage logs for at least seven years. Storage is cheap (especially digital), and the peace of mind is worth it. If you use a cloud-based mileage tracking app, your records are stored and backed up automatically.
10. Sample Mileage Log Entry
Here is an example of a single entry that contains all five required data points. This is the level of detail you should aim for with every business trip:
Sample Entry — January 15, 2026
Why this entry works: It includes the specific date, exact mileage (not a round number), a real street address as the destination, and a detailed business purpose that identifies the client and the nature of the meeting. This is precisely what an IRS examiner wants to see.
Additionally, you should record your annual odometer readings separately:
11. Common Mistakes That Get Mileage Deductions Denied
After reviewing the IRS requirements above, these are the most frequent errors that lead to reduced or disallowed mileage deductions during audits:
Claiming round numbers
If your log shows exactly 100 miles, then 200 miles, then 150 miles, it screams 'estimated.' Real trips produce odd numbers like 23.4 miles or 17.8 miles.
Logging trips for every single day including weekends and holidays
If your log claims 365 days of business driving with no gaps, it lacks credibility. Auditors know people take vacations and sick days.
Recording identical mileage for repeat trips
Even the same route varies slightly due to detours, traffic, and construction. Exact duplicates suggest entries were copied rather than recorded in real time.
Vague business purposes
Writing 'business' or 'work' is not specific enough. You need to state the business purpose clearly, such as 'Client meeting with Jane Doe at Acme Corp' or 'Picked up supplies for the Johnson renovation.'
Missing the January 1 odometer reading
The IRS requires your beginning-of-year and end-of-year odometer readings. Without them, the IRS cannot verify whether your claimed business percentage is reasonable.
Counting commuting miles as business miles
Driving from your home to your regular place of business (office, brokerage, etc.) is commuting, and it is never deductible — even if you make business calls during the drive.
Reconstructing the entire log at tax time
Sitting down in April to create a mileage log for the prior year based on your calendar is the single fastest way to lose a mileage deduction in an audit. This is the opposite of 'contemporaneous.'
Forgetting to separate personal stops during a business trip
If you drop off dry cleaning or stop at the grocery store in the middle of a business trip, those personal detour miles must be subtracted from the total.
12. How Automatic Mileage Trackers Solve the Compliance Problem
The core challenge with IRS mileage compliance is that the requirements are per-trip. If you make five business drives a day, five days a week, that is roughly 1,300 individual log entries per year — each requiring date, mileage, destination, and purpose. Very few people can maintain that level of manual discipline for an entire year.
This is the exact problem that automatic mileage tracking apps were built to solve. A well-designed app addresses each compliance requirement:
The result is a digital paper trail that is nearly impossible for an auditor to challenge. When an IRS agent sees a GPS-verified, timestamped log with classified trip purposes, they know the records are legitimate. Contrast that with a spreadsheet full of round numbers created on a single date — the difference in credibility is enormous.
For a detailed breakdown of the leading options and how they compare side by side, see our mileage tracker comparison page.
Key Takeaways
Vehicle expenses are one of the most commonly audited Schedule C deductions. If you claim mileage, expect to be asked for records.
IRC §274(d) and IRS Publication 463 require five data points for each business trip: date, mileage, destination, business purpose, and annual odometer readings.
"Contemporaneous" means recorded at or near the time of the trip. Logs created after the fact — especially at tax time — will be rejected.
The Cohan Rule does not save you. For vehicle expenses subject to §274(d), the IRS can disallow the entire deduction if records are inadequate.
Keep mileage logs for at least 3 years from filing (6 years if income understatement exceeds 25%). We recommend 7 years.
Automatic GPS-based mileage trackers create inherently contemporaneous records that satisfy all IRS requirements with minimal manual effort.
Mixed-use vehicle owners must calculate and document their business-use percentage using beginning and end-of-year odometer readings.
Avoid round numbers, vague purposes, and perfect patterns in your log — these are the red flags auditors look for first.
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