How do I claim mileage on my tax return?

HMRC's flat rate (Approved Mileage Allowance Payments) for 2025/26 is 45p per mile for the first 10,000 business miles and 25p per mile after that. To claim it: keep a mileage log recording the date, destination, purpose, and miles for each business journey; multiply your total business miles by the appropriate rate; include the total in your Self Assessment return as a business expense. You can't claim mileage and actual vehicle running costs at the same time — it's one or the other. The flat rate is usually simpler and works well for most people.