HMRC expects a record of each business journey showing the date, where you started and finished, why you made the trip and the miles driven. Employees claiming tax relief on mileage must send HMRC logs giving the reason and the start and end postcodes of every journey, and the self employed need the same evidence whether they use the flat mileage rate or claim a business share of actual running costs.

Why does HMRC want a mileage log at all?

Every mileage claim depends on one number: business miles. For the self employed, section 12B of the Taxes Management Act 1970 requires you to keep all records needed to make a correct and complete return, and for a trade those records must include all amounts received and spent and what each one was for. A person who fails to keep or preserve the records is liable to a penalty of up to £3,000 under section 12B(5).

The deduction rules also depend on evidence. Section 34 ITTOIA 2005 allows only expenses incurred wholly and exclusively for the trade, with an identifiable part or proportion allowed under section 34(2) where a vehicle is used for both business and private journeys. Without a log there is no reliable way to show that proportion, and in an enquiry an unsupported claim is easy for HMRC to reduce.

What should each entry in a mileage log show?

HMRC does not prescribe a form, and section 12B(4) allows records to be preserved in any form and by any means, so a notebook, spreadsheet or app all work. The content is what counts. A log that will stand up should show, for each journey:

  • the date
  • the start point and end point, ideally with postcodes
  • the business reason, such as the client visited or the site attended
  • the business miles
  • which vehicle was used, if you use more than one

The postcode and reason requirement comes directly from HMRC’s guidance for employees claiming relief: when you claim, you must send copies of your mileage logs showing the reason for every journey and the postcode for its start and end point, and a separate log for each employment if you claim for more than one. The self employed are not asked to send logs with their return, but building to the same standard means the log is ready if HMRC asks. It also helps to note the odometer reading at the start and end of each accounting period, which gives total miles for any apportionment.

What do the self employed need for the flat mileage rate?

Sole traders and partnerships of individuals can use simplified expenses for vehicles instead of claiming actual running costs. For the 2026 to 2027 tax year the rates are 55p a mile for cars and goods vehicles for the first 10,000 business miles and 25p after that, and 24p for motorcycles. The car and goods vehicle rate was 45p before 6 April 2026. HMRC’s policy paper explains that the increase was announced on 21 May 2026 and applies retrospectively from 6 April 2026, with legislation to substitute 55p in section 94F of ITTOIA 2005.

The flat rate cannot be used for a vehicle on which you have already claimed capital allowances or included in your expenses, and once you use it for a vehicle you must continue for as long as that vehicle is used in the business. Parking and other travel such as train fares are claimed on top. Under the flat rate, the mileage log is the only evidence for the whole deduction, so its quality decides the claim. The rates are explained further in simplified expenses.

What if you claim actual vehicle costs instead?

If you claim actual costs, HMRC’s guidance at BIM37600 is to allow the actual costs of trade journeys, such as fuel, tolls and parking, plus a proportion of the licence, insurance, repairs and finance costs. That proportion is normally business miles divided by total miles, so you need both figures, which is where the odometer readings come in. Keep fuel receipts, insurance schedules, service invoices and finance agreements alongside the log. The adjustment itself is covered in private use adjustments.

Which journeys can go in the log?

Only business journeys. For the self employed, HMRC’s list of costs you cannot claim includes non business driving and travel between home and work. For employees, relief does not include travelling to and from your work unless it is a temporary place of work. Whether a journey counts can be finely balanced, especially for people who work from home or move between sites, so the reason column is important: it shows why each trip was business. The rules on which journeys qualify are in travel expenses for the self employed.

What do employees and employers need to keep?

Employers can pay mileage allowance payments up to the approved amount, business miles multiplied by the approved rate, without reporting them. HMRC’s Employment Income Manual at EIM31390 says that even then the employer still needs to keep records of the payments made and the business journeys they relate to. Any excess over the approved amount is reported on form P11D and taxed. See approved mileage allowance payments.

If your employer pays less than the approved amount, or nothing, you can claim the difference as mileage allowance relief. HMRC says you need to keep records of the dates and mileage of your work journeys, add up the mileage for each vehicle type, and take away what your employer paid. You can claim for the current tax year and the four previous tax years, which is a good reason to keep logs from earlier years. If you file a Self Assessment return, you claim through the return.

How long should you keep the log?

Self employed people must keep business records for at least five years after the 31 January submission deadline for the tax year. Employees who file a Self Assessment return on time should keep records for at least 22 months after the end of the tax year. Employees who claim relief for earlier years outside Self Assessment need the logs for each year claimed.

A worked example

Illustration only. Leah, a self employed electrician, logs 12,000 business miles in her own van in the 2026 to 2027 tax year and uses the flat rate. Her claim is 10,000 miles at 55p, £5,500, plus 2,000 miles at 25p, £500, giving £6,000. Every one of those miles needs a dated entry with a reason.

Tom, an employee, drives 6,000 business miles in his own car and his employer pays 30p a mile, £1,800. The approved amount is 6,000 at 55p, £3,300. Tom can claim mileage allowance relief on the £1,500 difference, and must send his log with the claim.

What mistakes weaken a mileage claim?

  • Reconstructing the year’s journeys from memory or a diary after the year end, rather than logging as you go.
  • Claiming a round percentage of total miles with nothing behind it.
  • Including the regular journey between home and your normal place of work.
  • Switching a vehicle between the flat rate and actual costs from year to year.
  • Keeping one combined log when you have two employments, when HMRC asks for a log for each.
  • Discarding logs before the retention period ends.

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Sources

Reviewed by Christine Anderson, Broker, Solar Protect. Last reviewed 19 October 2026. Part of Accountapedia, the Solar Protect guide to UK tax and accounting. This page is general information, not personalised advice.