Mileage log app or spreadsheet?

A spreadsheet costs nothing and lets you write whatever you like. That is both its advantage and its problem. A mileage log is supposed to show what actually happened, and then it matters when the rows were written.

What a spreadsheet is good at

It is free, it syncs, and you can shape the columns however you want. If you make few business journeys a year and note them the same day, a spreadsheet is a perfectly real mileage log. Plenty of people manage well with one.

What it does not give you is the distance. You either read the odometer every time or look the route up in a map afterwards, and that is the part people stop doing first.

Where a spreadsheet is weak

Rows can be written, edited and deleted at any time, and nothing in the file shows that it happened. A spreadsheet filled in during one sitting for a whole year looks exactly like one kept journey by journey.

Since HMRC expects a contemporaneous record, that is precisely where a spreadsheet is weakest as evidence.

What the app does differently

The phone records the journey as it happens: start, finish, route and distance. You confirm the purpose with one tap.

Each journey is written into a log where every entry carries a fingerprint of the one before it. If an old journey is altered later the fingerprints no longer match, and the check shows exactly where. A mistake is corrected by a new entry pointing at the old one, and both stay visible.

You can still download the whole year as a spreadsheet when your accountant asks for one — the difference is how the rows came to exist.