If you drive for business and file a Self Assessment tax return, you can claim mileage to reduce your tax bill — yet thousands of taxpayers either skip the claim entirely or enter the wrong figure. This guide walks you through how to claim mileage on your Self Assessment return for 2026/27, including which forms to use, where to enter the amount, and how the rules differ for sole traders and employees.
Who Needs to Claim Mileage via Self Assessment?
Two groups of people claim mileage through Self Assessment, and the route is different for each.
Sole traders and self-employed workers deduct business mileage as an allowable expense on the self-employment pages of their return (SA103S or SA103F). The deduction reduces your taxable trading profit, which in turn lowers your income tax and Class 4 National Insurance bill.
Employees who file Self Assessment can claim Mileage Allowance Relief (MAR) if their employer reimburses them at less than the HMRC approved rate. You enter this on the employment pages of your return. If your total employment expense claims are under £2,500 and you do not otherwise need to file Self Assessment, you can use a P87 form instead.
In both cases, the HMRC approved mileage rate for cars and vans is 45p per mile for the first 10,000 business miles and 25p per mile after that. For a full breakdown of the current rates, see our guide to the HMRC mileage rate for 2026/27.
How Simplified Expenses Work for Mileage
Most sole traders use the simplified expenses method for vehicle costs. Instead of tracking every receipt for fuel, insurance, servicing and depreciation, you simply multiply your business miles by the HMRC flat rate and claim the total.
Here is how the calculation works:
- First 10,000 business miles: 10,000 × 45p = £4,500
- Each mile above 10,000: additional miles × 25p
The alternative is the actual costs method, where you work out the real running costs of your vehicle and claim the business-use proportion. You must choose one method when you first start using a vehicle for business, and you cannot switch that vehicle between methods later. Our actual costs vs mileage rate comparison explains when each method makes sense.
One important restriction: if you have already claimed capital allowances on a vehicle, you cannot use simplified expenses for that same vehicle. You are locked into actual costs.
Step-by-Step: Entering Mileage on Your Self Assessment Return
Sole Traders — SA103 Self-Employment Pages
When you file your Self Assessment online through your HMRC Government Gateway account, you will complete either the SA103S (short) or SA103F (full) supplementary pages for self-employment income.
- Navigate to the Self Employment section of your online return.
- Find “Car, van and travel expenses” under Allowable business expenses. This is the line where your mileage claim goes.
- Calculate your total claim. Multiply your business miles by the appropriate rate. If you drove 12,000 business miles: (10,000 × 45p) + (2,000 × 25p) = £4,500 + £500 = £5,000.
- Enter £5,000 in the Car, van and travel expenses box.
- Do not submit your mileage log with the return — HMRC does not ask for it at filing time. However, you must keep it for at least five years after the 31 January submission deadline, in case HMRC opens an enquiry.
If you also claim passenger payments (5p per business mile for each employee or colleague you carry), add that amount to the same box.
Employees — Mileage Allowance Relief on the Employment Pages
If you are an employee who files Self Assessment, go to the Employment section and tick the box indicating you have expenses to claim for that employment.
Look for “Other expenses and capital allowances” or a dedicated mileage line — the exact wording varies depending on whether you use the online portal or commercial software.
Enter the MAR amount, which is the shortfall between the HMRC approved rate and what your employer actually paid you.
Worked example: You drove 8,000 business miles during 2026/27. Your employer reimbursed you at 20p per mile.
- HMRC approved amount: 8,000 × 45p = £3,600
- Employer paid: 8,000 × 20p = £1,600
- MAR claim: £3,600 − £1,600 = £2,000
This £2,000 reduces your taxable employment income. At the basic rate of 20%, that is a £400 tax saving. A higher-rate taxpayer would save £800.
If your employer paid you nothing at all for business mileage, the full £3,600 is your MAR claim.
When to Use a P87 Form Instead of Self Assessment
Not every employee needs to file a full Self Assessment return to claim mileage relief. If all of the following apply, you can use the simpler P87 route:
- You are an employee (not self-employed).
- Your total employment expenses claim is £2,500 or less.
- You do not already need to file Self Assessment for another reason (such as rental income or self-employment).
You submit the P87 online through your Personal Tax Account. HMRC will adjust your tax code so you pay less tax going forward, or issue a refund for overpaid tax. Our guide to HMRC mileage allowance relief via P87 walks through the full process.
If your expenses exceed £2,500, you must register for Self Assessment and file a return instead.
Making Tax Digital: What Changes from April 2026
Making Tax Digital for Income Tax (MTD for ITSA) launches in April 2026 for sole traders and landlords with qualifying income above £50,000. From April 2027, the threshold drops to £30,000, and from April 2028 it falls further to £20,000.
Under MTD, you must:
- Keep digital records of all income and expenses using HMRC-recognised software.
- Submit quarterly updates to HMRC (deadlines: 7 August, 7 November, 7 February and 7 May).
- File a final declaration by 31 January, replacing the traditional Self Assessment return.
For mileage, this means your trip log must be in digital format and linked to your MTD-compatible software. Paper notebooks and standalone spreadsheets without an approved digital link no longer meet the standard. Tripbook records every business trip automatically via GPS tracking, and you can export your data directly into MTD-compatible accounting software — so your mileage records stay compliant without extra admin.
HMRC has confirmed it will not issue penalty points for late quarterly updates during the first year (2026/27), but penalties still apply for late final declarations and late payment.
What Records You Must Keep
Whether you file under traditional Self Assessment or MTD, HMRC expects you to maintain a mileage log that records:
- Date of each business journey
- Start and end locations
- Business purpose of the trip
- Miles driven
You do not need to record odometer readings, but the log must be contemporaneous — meaning you record trips as they happen, not reconstructed months later at tax time.
Records must be kept for at least five years after the 31 January filing deadline. For the 2026/27 tax year (deadline 31 January 2028), that means holding records until at least January 2033.
Tripbook makes this straightforward. The app logs trips in the background using your phone’s GPS, lets you classify each trip as business or personal with a single swipe, and stores everything securely. When your tax return is due, you export a summary showing your total business miles and the calculated claim — ready to enter on your return.
Download Tripbook from the App Store and start building your mileage log now.
Common Mistakes That Cost You Money
Forgetting the 10,000-mile threshold. The rate drops from 45p to 25p after 10,000 business miles. If you drove 14,000 miles and claimed the full amount at 45p, HMRC may query your return. Equally, if you only claimed 25p on all miles, you have underclaimed.
Claiming your commute. Travel between your home and your regular place of work is never an allowable business expense. Temporary workplace journeys and client visits do qualify.
Mixing up simplified and actual costs. Once you choose a method for a vehicle, you are committed. You cannot switch to simplified expenses later if you started with actual costs, or vice versa.
Missing the deadline. The online Self Assessment deadline for 2026/27 is 31 January 2028. Paper returns must reach HMRC by 31 October 2027. Late filing triggers an automatic £100 penalty, even if you owe no tax.
Not claiming at all. If your employer pays you nothing for business mileage — or less than 45p per mile — you are leaving money on the table. Check whether a P87 or Self Assessment claim could put money back in your pocket.
If you missed a mileage claim in a previous tax year, you can amend your return up to four years after the end of that tax year. Employees not on Self Assessment can submit a P87 for the earlier year.
