What If I Didn’t Keep Track of My Mileage for Business Expenses?

Tracking mileage is essential for claiming business-related vehicle expenses, but many people fail to keep accurate records. Without proper documentation, proving deductions can be difficult, especially if the IRS requests evidence.

If you didn’t track mileage, you may still estimate and support your deduction, but relying on reconstructed records carries risks. The IRS may reduce or reject your claim during an audit if the evidence is insufficient.

IRS Requirements for 2025 Filings

The IRS requires detailed records to deduct business mileage. For 2025 filings, taxpayers must maintain a log that includes the date, purpose, and miles driven for each business trip. These records should be kept contemporaneously—recorded at or near the time of travel. Without proper documentation, deductions may be denied if audited.

The standard mileage rate for 2025 is 67 cents per mile, an increase from the previous year due to inflation. This rate applies to self-employed individuals, gig workers, and certain employees. Those using the actual expense method must keep receipts for fuel, maintenance, insurance, and depreciation, following IRS Publication 463.

Taxpayers must also separate personal and business use of a vehicle. Only the business portion is deductible, calculated as a percentage of total miles driven. If records are incomplete or personal miles are included in error, deductions may be reduced or disallowed.

Estimated Mileage Reconstruction

If mileage records were not maintained, estimates can be made using available data. Reviewing past appointments, client meetings, or job sites can help establish travel patterns. Calendar entries, emails, and invoices can provide a basis for estimating miles driven. For example, a consultant who visited a client’s office twice a week can calculate the round-trip distance and multiply it by the number of visits.

GPS data from mobile devices or vehicle tracking apps can also help. Many smartphones log location history, which can serve as supporting evidence. Ride-hailing drivers can retrieve trip histories from platforms like Uber or Lyft to approximate business miles. Similarly, credit card statements showing fuel purchases at specific locations can help establish a travel pattern when combined with other records.

Toll records and parking receipts provide additional proof of vehicle use. A business owner attending industry conferences or networking events can use transaction histories from toll booths or parking garages to substantiate travel. Maintenance records from auto shops, which often include odometer readings, can help determine total miles driven and support a reasonable business-use allocation.

Alternative Documentation

When precise mileage logs are unavailable, other records can help validate business-related vehicle expenses. Bank and credit card statements showing fuel purchases at regular intervals can demonstrate consistent vehicle use. If purchases align with a predictable work schedule, they can support a reasonable mileage estimate. Expense reports submitted to clients or employers, particularly those including travel reimbursements, may also serve as verification.

Business communications can further strengthen claims. Emails discussing travel plans, contracts specifying on-site obligations, or client invoices referencing in-person meetings contribute to a credible mileage estimate. A real estate agent might use property showing schedules, while a field technician could reference work orders detailing service calls. Cross-referencing these documents with other records helps establish business-related driving patterns.

Accounting software that tracks business expenses may contain travel-related entries. Some businesses use fleet management software or apps that monitor employee travel, generating reports to substantiate mileage claims. Even social media posts documenting business trips can serve as informal proof when combined with other records.

Potential Impact on Deductions

Without a well-documented mileage log, business vehicle expense deductions may be reduced. The IRS allows deductions based on either the standard mileage rate or actual expenses, but both require substantiation. If records are incomplete or estimates appear inconsistent, the IRS may disallow portions of the deduction, requiring additional supporting evidence. This can be particularly problematic for self-employed individuals and small business owners who rely on vehicle expenses to offset taxable income.

Reconstructed mileage estimates often result in a more conservative deduction since indirect records replace precise documentation. Tax professionals typically recommend claiming the lowest reasonable estimate to reduce the risk of penalties if the IRS challenges the claim. For example, if a taxpayer believes they drove 10,000 miles for business but can only substantiate 7,500 through alternative documentation, claiming the lower amount minimizes potential tax liabilities. Overstating mileage without proper evidence could trigger accuracy-related penalties under Internal Revenue Code 6662, which imposes a 20% penalty on underpayments due to negligence or substantial understatement of income.

Audit Ramifications

Failing to maintain proper mileage records increases the likelihood of scrutiny if the IRS audits a return. Mileage deductions are frequently examined because they are often overstated or lack sufficient documentation. If audited, the IRS will request supporting evidence to verify business-related travel. Without a contemporaneous log, taxpayers must rely on reconstructed records and alternative documentation, which may not always meet IRS standards. Examiners will compare reported mileage with fuel purchases and business income to assess whether the claim is reasonable.

If the IRS finds discrepancies or considers the mileage estimate unreliable, it may reduce or deny the deduction. In cases of significant misreporting, additional penalties may apply. Under Internal Revenue Code 6662, taxpayers who underpay due to negligence or substantial misstatements face a 20% penalty on the underpaid amount. If the IRS determines the misstatement was intentional, fraud penalties under Internal Revenue Code 6663 could apply, leading to a 75% penalty on the portion of tax underpaid due to fraudulent intent. While criminal prosecution is rare, cases involving fabricated records or deliberate misrepresentation could result in legal consequences.