Mileage tracker app vs a spreadsheet or notes app

What the IRS actually requires

Per IRS Publication 463, a compliant mileage record needs four elements for every trip: date, business destination, business purpose, and mileage. There's no requirement that it come from an app — a notebook, a spreadsheet, or a notes app entry all count, as long as the record is contemporaneous (made at or near the time of the trip, not reconstructed months later from memory).

Where hand-kept logs tend to fail in practice

• Missing trips, not wrong trips. A spreadsheet only has what you remembered to type in. On a slow night or a rushed shift, logging the trip is the first thing that gets skipped — and a skipped entry doesn't show up as an error, it just isn't there.
• Odometer readings, not estimates. "About 8 miles" typed from memory a day later is weaker evidence than a GPS-measured distance if a log is ever questioned. See what an audit actually asks for.
• No running total. The business-use percentage that Schedule C Part IV asks for needs a beginning- and end-of-year odometer reading most spreadsheet-based drivers don't have on hand.

When a spreadsheet is genuinely enough

A driver who drives on a fixed schedule, rarely forgets to log a trip, and is disciplined about odometer readings can keep a fully compliant log for free with no app at all. The trade-off an automatic tracker is selling isn't legality — it's consistency over a full year, which is a habit problem more than a paperwork problem.