--- title: "Audit trail" description: "An audit trail is the chronological record behind a transaction. What it is for, what the IRS expects in a travel expense record and how long to keep it." canonical: https://engine.com/glossary/audit-trail updated: 2026-11-02 author: "Engine Editorial" --- # Audit trail An audit trail is a chronological record that lets someone reconstruct the sequence of activities behind a transaction, from its start to its result. Updated November 2, 2026 by Engine Editorial ## What is an audit trail? An audit trail is the record that shows how a transaction happened, step by step. This cheat sheet covers how to think about one and what to check in your own records. The detail is further down. ### How to think about it - **It's a sequence, not a pile.** An audit trail is a chronological record. Its job is to let someone reconstruct a transaction from start to result. - **Record it near the time.** The IRS says a timely kept record has more value than a statement prepared later, when recall is less accurate. - **Digital records count.** Under IRS rules, a record prepared on a computer is considered an adequate record. - **A statement line isn't the whole story.** Card statements show dates, amounts and vendor names, without the itemization or business context behind a charge. ### What to check - **Business purpose.** The IRS generally expects a written statement of the business purpose of an expense, unless the purpose is clear from the circumstances. - **Hotel receipts.** A hotel receipt supports a business trip when it shows the hotel's name and location, the dates of the stay and separate amounts for lodging, meals and phone calls. - **Approvals.** Verbal approvals leave no evidence of who authorized the spend. - **Retention.** Keep records that support a tax return until that return's period of limitations runs out, generally 3 years unless a longer period applies. ## What the IRS expects in a travel expense record | Element | What to record for travel | | --- | --- | | Amount | The cost of each separate expense for travel, lodging and meals. Incidentals can be totaled in reasonable categories, such as taxis or fees and tips | | Time | The dates you left and returned, and the number of days spent on business | | Place | The destination, such as the name of the city or town | | Business purpose | The business purpose for the expense, or the business benefit gained or expected | ## How it works on Engine Engine [travel reporting](https://engine.com/features/travel-reporting-analytics) uses booking and billing data captured in the platform, and company fields such as department, project, job code and cost center add the context for filtering and reconciliation. With [Engine Approvals](https://engine.com/features/engine-approvals), a traveler gives a reason for an out-of-policy request, and the approver approves and books or declines with a reason. Engine's [accounting integrations](https://engine.com/accounting-integrations) sync transactions to QuickBooks Online, NetSuite or Sage Intacct, and each synced transaction can be traced back to its source in Engine. ## Keep the context with the booking Engine reporting uses booking and billing data captured in the platform, with fields like department, project and cost center for filtering and reconciliation. Free to use. [Get started](https://engine.com/sign-up) ## Questions ### What is the purpose of an audit trail? To let someone reconstruct and examine the sequence of events behind a transaction, from start to result. For a business trip, the IRS elements to prove are the amount, the time, the place and the business purpose. ### How long should you keep expense records? Generally until the period of limitations for that tax return runs out. The IRS says 3 years in most cases, and 7 years if you claim a loss from worthless securities or a bad debt deduction. ### Do you need a receipt for every expense? Not for every one. The IRS doesn't require documentary evidence such as a receipt for an expense under $75 unless it is lodging, but you still need a record of the expense. ### Can you estimate expenses if records are missing? No. Under IRS rules you can't deduct amounts you approximate or estimate. With incomplete records, you need your own specific statement plus other supporting evidence. ## Go deeper - [Audit-ready travel data](https://engine.com/blog/audit-ready-travel-data-build-compliance-into-every-booking) - [Engine travel reporting and analytics](https://engine.com/features/travel-reporting-analytics) - [Expense report](https://engine.com/glossary/expense-report) - [Itemized receipt](https://engine.com/glossary/itemized-receipt) ## Sources 1. NIST Computer Security Resource Center, "audit trail," https://csrc.nist.gov/glossary/term/audit_trail, accessed November 2, 2026. 2. Internal Revenue Service, "Publication 463 (2025), Travel, Gift, and Car Expenses," https://www.irs.gov/publications/p463, accessed November 2, 2026. 3. Internal Revenue Service, "How long should I keep records?," https://www.irs.gov/businesses/small-businesses-self-employed/how-long-should-i-keep-records, accessed November 2, 2026. 4. Engine, "Audit-Ready Travel Data: Build Compliance Into Every Booking," https://engine.com/blog/audit-ready-travel-data-build-compliance-into-every-booking, accessed November 2, 2026. 5. Engine, "Travel Reporting and Analytics," https://engine.com/features/travel-reporting-analytics, accessed November 2, 2026. 6. Engine, "Approval Workflows for Out-of-Policy Bookings," https://engine.com/features/engine-approvals, accessed November 2, 2026. 7. Engine, "Accounting Integrations," https://engine.com/accounting-integrations, accessed November 2, 2026.