46 — Written Evidence to Support Deduction Updated for tax year 2025

What this line means

A yes-or-no question asking whether you have written evidence (such as a mileage log) to support your vehicle deduction. The IRS requires contemporaneous written records — a log created at or near the time of each trip — showing the date, destination, business purpose, and miles driven. Answering “no” does not prevent you from claiming the deduction, but it signals to the IRS that your records may not withstand audit scrutiny.

Does this apply to you?

• You claim car and truck expenses on line 9
• You complete Part IV for your business vehicle
• You keep (or should keep) a mileage log or similar record

Easy to overlook

“Written evidence” means a contemporaneous log A mileage log created at the time of each trip satisfies the requirement. A summary reconstructed at year-end from memory or calendar entries does not. The IRS specifically looks for records made at or near the time of the expense. Digital mileage tracking apps that log trips automatically are the most reliable form of evidence. ¹ [SOURCE: IRS Publication 463 — Travel, Gift, and Car Expenses]

Answering “no” is an audit invitation While the IRS does not automatically disallow your deduction for answering “no,” this answer tells them your documentation is weak. If your return is selected for examination, vehicle expenses without written evidence are among the easiest deductions for the IRS to deny completely. ² [SOURCE: Audit pattern — vehicle expense deductions without mileage logs]

Watch out for this

Answering “yes” without actually having adequate records. If you answer “yes” and are audited, the IRS will ask to see the log. Claiming you have written evidence when your only record is a year-end estimate undermines your credibility and can lead to penalties for negligence on top of losing the deduction.

Related lines on your return

• Line 47a — Schedule C — Whether written evidence was made at the time of expense
• Line 44a — Schedule C — Business miles; the number your written evidence must support
• Line 9 — Schedule C — Car and truck expenses; the deduction that depends on this evidence