Corporate Policy
Producing the elements required to prove an expense: date, amount, purpose, place.
Substantiation is the formal presentation of the elements that prove a mileage expense: date, distance, origin, destination, specific business purpose. IRS Publication 463 defines "adequate" substantiation as a contemporaneous record (or near-event), written documentation, and corroborative evidence (receipt, map, GPS log). Reconstructed assertions made later rarely survive an audit.