Do I Need to Keep a Mileage Log? What HMRC Actually Requires

If you claim mileage on your Self Assessment tax return, you probably assume HMRC will just take your word for it. Most of the time, they do. But if you're selected for a compliance check (and thousands of people are every year), you'll need to prove every mile you claimed.

The short answer: yes, you need records

HMRC doesn't require you to submit a mileage log with your tax return. But they do require you to keep records that support your claim. If they ask, you need to be able to show:

• The date of each business journey
• Where you went (start and end points)
• The purpose of the journey (why it was business-related)
• The distance in miles

This is spelled out in HMRC's guidance on record-keeping for the self-employed. You must keep records for at least 5 years after the 31 January submission deadline for that tax year.

What counts as a valid record?

HMRC doesn't prescribe a specific format. Any of these would satisfy a compliance check:

• A digital mileage log: an app like KeptMiles that records date, route, distance, and purpose automatically.
• A spreadsheet, manually maintained with the same fields. Tedious but valid.
• A paper notebook, the old-school approach. Works, but easy to lose and hard to total up.

What doesn't work: a round number on your tax return with nothing to back it up. "I drove about 8,000 business miles" with no supporting records is exactly what triggers HMRC's interest.

What happens if you can't prove it?

If HMRC opens a compliance check and you can't produce records, they can:

• Reduce your claim. They'll estimate what they think is reasonable, which is usually less than what you claimed.
• Charge interest on any underpaid tax from the adjustment.
• Apply a penalty of up to 30% of the tax underpaid for "careless" errors. More if they consider it deliberate.

The penalty is the real sting. Even if you genuinely did drive those miles, without evidence HMRC treats it as a careless error. And "I forgot to keep records" isn't a defence.

Types of HMRC compliance checks

Not all compliance checks are the same. HMRC runs several types, and the one you get determines how much of your records they'll want to see:

• Aspect enquiry: the most common type. HMRC picks one specific area of your return to question. For mileage claims, this usually means they want to see your journey records and how you arrived at the total on your SA103. This is the kind of check where having a proper mileage log makes all the difference. You hand over your records and it's done.
• Full enquiry: much rarer and more invasive. HMRC examines your entire return, including all income sources, expenses, bank statements, and records. These are typically triggered by significant inconsistencies, for example claiming high mileage but declaring low income, or a lifestyle that doesn't match reported earnings.
• Random check: HMRC selects a percentage of returns at random, regardless of whether anything looks suspicious. You can do everything right and still be picked. Exactly why keeping records matters even if you think your claim is straightforward.

HMRC opened over 300,000 compliance checks in the 2023/24 tax year. The majority were aspect enquiries, but even those can result in penalties, interest, and adjusted claims if your records are inadequate.

What triggers a compliance check?

HMRC uses a system called Connect that cross-references data from multiple sources: bank records, third-party reports, and historical filing patterns. Common triggers for mileage-related checks include:

• Round numbers. Claiming exactly 10,000 miles or exactly £4,500 in mileage is a red flag. Real mileage totals are messy numbers like 9,847 or 11,263.
• Sudden jumps. If you claimed 5,000 miles last year and 12,000 this year with no obvious change in your business, HMRC will want to know why.
• High mileage relative to income. A sole trader reporting £25,000 income but claiming 20,000 business miles raises questions about the nature of the business.
• Inconsistency with your trade. HMRC has benchmarks for typical mileage by profession. A desk-based IT consultant claiming the same mileage as a mobile plumber will stand out.
• Late or amended returns. Filing late or amending previous returns draws more scrutiny to all parts of your return, including expenses.

Understanding HMRC penalties

If HMRC finds an error in your mileage claim, the penalty depends on how they classify it. The penalty framework works on a sliding scale:

• Careless (0–30%): you didn't take reasonable care. For mileage, this means you didn't keep proper records or made errors that basic record-keeping would have prevented. Failing to keep a mileage log at all falls into this category. The actual percentage depends on whether you tell HMRC about the error yourself (lower end) or they discover it (higher end).
• Deliberate (20–70%): you knew the claim was wrong. Claiming personal journeys as business, inflating distances, or fabricating trips. The range is wide because HMRC considers whether you helped during the investigation and whether you told them voluntarily.
• Deliberate and concealed (30–100%): you not only made a false claim but took steps to hide it. Creating fake records, destroying evidence, or using a second set of books. The most serious category, and it can lead to criminal prosecution in extreme cases.

In HMRC's language, "careless" doesn't mean you were dishonest. It means you didn't take the care that a reasonable person would. Not keeping a mileage log when you're claiming thousands of pounds in mileage allowance is, by definition, careless. Even if every mile was genuine.

The penalties are calculated as a percentage of the potential lost revenue: the extra tax HMRC would have collected if the error hadn't been made. So if your mileage claim was £2,000 too high and you're a basic rate taxpayer, the potential lost revenue is £400 (20% tax). A 30% careless penalty on that is £120, on top of repaying the £400 plus interest. For a higher rate taxpayer, the same overclaim produces £800 in potential lost revenue, and a 30% penalty of £240.

What happens if you can't produce records at all

This is the worst-case scenario, and it's more common than you'd think. HMRC asks for your mileage records, and you have nothing: no log, no spreadsheet, no diary entries. What typically happens:

1. HMRC makes their own estimate. They'll look at the nature of your business, your income, your location, and what they consider "typical" for your trade. Their estimate is almost always lower than what you actually drove, because they have no reason to be generous.
2. You can't effectively challenge the estimate. Without records, you have no basis to argue. You might know you drove 12,000 business miles, but if HMRC estimates 7,000 and you have no evidence, 7,000 is what sticks.
3. The adjusted tax is calculated. The difference between your original claim and HMRC's estimate generates extra tax owed, plus interest from the original filing date.
4. A penalty is applied. The lack of records is automatically classified as "careless" at minimum. If HMRC believes you had records and didn't produce them, it can escalate to "deliberate."

A plumber who claimed 11,000 business miles (£4,750 in mileage allowance) but can't produce any records might see HMRC estimate 6,000 miles (£2,700). That's £2,050 in disallowed expenses. At the basic tax rate, that's £410 extra tax, plus interest, plus a careless penalty of up to £123. Total cost: potentially over £500, all because there was no log.

How long a compliance check takes

Don't expect a quick resolution. An aspect enquiry into mileage typically takes 3 to 12 months from the initial letter to final settlement. If your records are clean and you respond promptly, it can be wrapped up in a few weeks. If there are problems (missing records, inconsistencies, disputes) it drags on.

A full enquiry can take 12 to 18 months or longer. During this time, HMRC may request multiple rounds of documents, ask detailed questions about specific journeys, and cross-reference your records with bank statements and client invoices.

The stress and time cost of a compliance check is significant even if the outcome is in your favour. Having organised, detailed records from the start means you can respond quickly, keep the process short, and avoid escalation.

Digital vs paper records: what HMRC actually prefers

HMRC doesn't officially mandate digital records for mileage (unless you're in Making Tax Digital). But in practice, digital records carry more weight in a compliance check for several reasons:

• Timestamps are automatic. A GPS-based log creates records at the time of the journey with verifiable timestamps. A paper notebook could have been written at any time, including the night before you received HMRC's letter.
• GPS data is verifiable. Coordinates and routes can be independently checked. Paper records rely entirely on your word.
• Digital records are harder to fabricate. Creating a year's worth of fake GPS data with realistic timestamps, locations, and routes is extremely difficult. Writing a year's worth of fake notebook entries takes an afternoon.
• Consistency is built in. An automatic tracker records every journey, every day, whether you remember or not. Paper logs have gaps (holidays, busy weeks, the months you forgot), and those gaps undermine the credibility of the entries that are there.
• Search and export. When HMRC asks about a specific journey on a specific date, you can find it in seconds. With a paper log, you're flicking through pages hoping your handwriting from eight months ago is legible.

Under Making Tax Digital (which now applies to self-employed individuals earning over £50,000), digital records are a legal requirement, not just a preference. And the threshold drops to £30,000 from April 2027. The direction of travel is clear: digital records are becoming the standard.

How far back do I need records?

HMRC can open a compliance check for any of the last 4 tax years (6 years if they suspect carelessness, 20 years if they suspect fraud). In practice, you should keep records for at least 5 years after the 31 January deadline for that tax year.

For example, mileage records for the 2025/26 tax year (ending 5 April 2026) should be kept until at least 31 January 2032.

The 6-year window for "careless" errors is the catch most people miss. If you didn't keep proper records, which is itself careless, HMRC can look back further than the standard 4 years. That means your 2020/21 records could still be requested today. If you've already thrown them away, there's nothing you can do about past years. But you can make sure this year onwards is properly documented.

Start now, not at tax time

The worst time to start keeping mileage records is January, when you're scrambling to file your return. The best time is now, before the new tax year starts on 6 April.

Set up automatic tracking, let it run in the background, and classify your journeys as you go. When Self Assessment time comes around, your records are already done. Export a report, hand it to your accountant, and move on. For a breakdown of what you can claim, see the guide to HMRC mileage rates for 2026/27.

Automatic mileage tracking with GPS. Every journey logged, every record kept.