How to keep a mileage log that stands up

A mileage claim is only as good as the log behind it. If you can't say where you went and why, a figure like "9,400 business miles" is just a number. Here's how to keep a record you'll be glad of at tax time.

What to write down

For each business journey:

• The date
• Where you started and where you went, with the address or a place name
• Why you went: the client, the job, the supplier
• The miles for the trip

Then, for the year as a whole:

• The vehicle you used
• The odometer reading on the first and last day of the tax year, so you can show your total miles and the business share of them

Three ways to keep it

A notebook in the glovebox. Simple and cheap, and it works if you're disciplined. The weak point is that you have to remember to write it down at the time, and paper gets lost.

A spreadsheet. Easy to total, easy to back up, and you can add columns for the vehicle and the client. The weak point is the same: someone has to type the entries, usually at the end of a long day.

An app that logs drives for you. Phone-based apps can notice a drive, record where it started and finished, and ask you whether it was for work. That cuts out the remembering. The things to check are how well it copes in the background, what it does with your location data, and whether it keeps working if the phone is switched off. Thistle Miles, which is in development, is designed to log work drives by itself and warn you if logging ever stops.

Whichever you use, the best method is the one you'll actually keep doing.

Habits that keep it accurate

• Write it up the same day. The detail is gone surprisingly quickly.
• Round honestly. Use the odometer or a map for the miles, and be consistent about how you measure.
• Note the reason, not just the place. "Site visit, Mrs Hughes, kitchen quote" tells a better story than "Leith".
• Separate private journeys. If you use the vehicle privately as well, keep your business log clean so you can show the split.
• Back it up. A photo of each notebook page, or a copy of the spreadsheet in another place, is cheap insurance.

Mistakes that weaken a log

• Rebuilding it from memory at year end. It looks reconstructed, because it is.
• Round numbers everywhere. A column of 20s and 30s is harder to trust than real distances.
• No reason for the trip. A record with no purpose can't show a journey was for business.
• Mixing in the commute. Your regular journey to a fixed workplace generally isn't a business journey.
• Changing methods midway. If you use simplified expenses for a vehicle, you stick with that method for it, so keep the log consistent.

What the log is for

Once you have it, the log lets you work out your claim and show how you got there. For the 2026/27 rates and how they work, see HMRC mileage rates for the self-employed. And if you want your invoices and mileage in one tidy place, the self-employed page shows how Thistle Invoice and Thistle Miles fit together.

Keep the log with your other records for at least five years after the 31 January Self Assessment deadline for that tax year. This is general information, not tax advice.