Six months is the DOT retention period — but IFTA requires records to be maintained for 4 years from the due date of the return or the filing date, whichever is later. Interstate operators must meet the longer requirement.

Both requirements must be satisfied. IFTA licensees are required to retain trip sheets, fuel receipts, and mileage records for the full 4-year retention period — not the DOT minimum of 6 months.

Regardless of route type — local or long-haul — operators of qualified motor vehicles are required to maintain odometer readings. Local operation does not exempt a carrier from documentation requirements.

Beginning and ending odometer readings should be recorded for each trip, regardless of distance traveled. In an audit, missing odometer records can result in estimated assessments and additional tax liability.

Submitting estimated mileage on IFTA returns is risky. During an audit, if your records don't support the miles reported, the auditor will calculate mileage using their own methodology — and the result is rarely in the carrier's favor.

IFTA requires that distance be supported by individual trip records showing origin, destination, route, and miles per jurisdiction. Without adequate documentation, auditors may assess additional tax, penalties, and interest based on their own calculations.