HMRC mileage calculator.

How HMRC’s 45p and 25p rates work

HMRC’s Approved Mileage Allowance Payment (AMAP) is 45p per mile for the first 10,000 business miles in a tax year, then drops to 25p per mile thereafter. The drop is per-tax-year, not per-job — if you do 9,000 miles by October you’ll switch into the 25p band somewhere mid-November. A “business trip” means travel from your base of work (usually your home or yard) to a customer site, or between customer sites in one day. It does notinclude your commute to a fixed workplace, even if that workplace is a building site. Motorbikes are 24p flat; bicycles are 20p flat with no 10k threshold. The rates cover fuel, wear and tear, insurance, and depreciation combined — you can’t claim them on top of separate fuel receipts.

What records HMRC actually requires

You need a contemporaneous mileage log — meaning recorded at the time, not reconstructed in March. For each business trip: the date, the start postcode (or address), the destination postcode, the business purpose (“site visit to Mrs Khan” counts; “work” doesn’t), and the mileage. If HMRC opens an enquiry they will ask to see this log, and reconstructed-from-memory logs are the single most common reason mileage claims are partially disallowed. Keep the log for at least six years after the tax year it relates to. A spreadsheet works; a notes app works; a dashcam with GPS works. What doesn’t work is a round-number estimate at year-end.

Common mileage claim mistakes that trigger HMRC queries

Three patterns cause most of the queries: (1) claiming home-to-fixed-workplace travel — if you work at the same site for more than 24 months, HMRC treats it as a permanent workplace and the commute stops being deductible; (2) claiming all miles on a personal vehicle without splitting business and personal use — if your van is also the family car at weekends, only the business portion is allowable; (3) round numbers across the year — a log showing exactly 1,000 miles every month gets flagged because real driving doesn’t look like that. The fix for all three is the same: log each trip at the time, separate clearly from personal use, and don’t round up.