Van costs, parts mark-up, diagnostic tools and the VAT threshold trap explained for mechanics who bring the garage to the customer.
A mobile mechanic carries two things most other sole traders do not: a vehicle that is simultaneously their transport, their workshop and one of their largest tax deductions, and a steady flow of parts they buy at trade price and re-charge to customers. Both of these create tax decisions that the generic "self-employed" guides skate over. Get the van treatment right and you protect your single biggest deduction. Get the parts treatment wrong and you can drift over the VAT threshold without realising it, because HMRC counts the full price you charge for a clutch or a cambelt kit as your turnover, not just the labour to fit it.
There is also one piece of genuinely good news compared with the building trades: there is no Construction Industry Scheme to navigate. Nobody deducts 20% before paying you, so every job lands in your account gross. That simplicity has a sting in the tail, though, because it means the entire tax and National Insurance liability is yours to ring-fence and pay. This guide is written for that reality.
As a sole trader you are taxed on your profit, not your turnover. Profit is everything you invoice (labour plus any parts you charge on) minus your allowable expenses. That profit figure then drives two charges. Income Tax is nil on the first GBP 12,570 (your personal allowance), 20% on profit up to GBP 50,270, and 40% above that into the higher-rate band. Class 4 National Insurance is 6% on profit between GBP 12,570 and GBP 50,270, then 2% on anything above. Class 2 NIC is no longer a separate flat weekly charge from 2024/25, though paying it voluntarily can still protect your state pension record if your profits are low.
You report all of this through Self Assessment, filing online by 31 January after the tax year ends. If you started trading and have not filed before, you must tell HMRC by 5 October in your second tax year of trading. Run your numbers through the sole trader tax calculator before January so the bill is never a surprise.
If you also do PAYE work, for instance a few employed shifts at a garage alongside your mobile rounds, your tax code on the employment may already be using your personal allowance. It is worth a moment to check your tax code so HMRC has not split your allowance in a way that leaves you under-taxed during the year and facing a catch-up bill.
For a mobile mechanic the van is the business, so how you treat it is the most important tax decision you will make. There are two methods and you must commit to one per vehicle.
The simplified mileage method lets you claim 45p per business mile for the first 10,000 miles in the tax year, then 25p per mile above that. You keep a mileage log instead of a folder of fuel receipts. This is clean and simple, but it bundles everything (fuel, insurance, servicing, depreciation) into that single rate, so you cannot also claim those costs separately.
The actual cost method lets you claim the genuine running costs of the van (fuel, insurance, servicing, MOT, road tax, repairs, breakdown cover) apportioned for any private use, plus a capital allowance on the van itself. For a mechanic this method often wins, because a working van does heavy mileage, needs frequent servicing, and the vehicle can be written off in full through the AIA in the year you buy it.
Use the mileage tax calculator to compare the two methods on your real numbers. As a rule of thumb, a higher-mileage, higher-maintenance van leans towards actual costs, while a newer, cheaper-to-run van on moderate mileage often does better on the flat rate. Whichever you choose, you keep that method for as long as you own that vehicle; you cannot flip back and forth year to year for the same van.
One trap specific to mechanics: the journey from home to your first job of the day is generally an ordinary commute and not a business mile, unless your home is genuinely your business base (which, for a mobile mechanic storing tools and stock at home and dispatching from there, it usually is). If home is your base, log it as such consistently. The journeys between customers during the day are always business miles.
Every expense must be incurred wholly and exclusively for the business. For a mobile mechanic the list is long because you are effectively running a workshop out of a vehicle.
| Expense category | What counts | Notes |
|---|---|---|
| Parts and consumables re-charged to customers | Filters, oil, brake pads, belts, fluids, fasteners bought at trade price | Deductible in full as cost of sales; the price you charge for them is taxable turnover |
| Workshop consumables | Rags, brake cleaner, grease, gloves, cable ties, threadlock | Deductible as used |
| Hand tools | Sockets, spanners, torque wrenches, prybars, jacks | Frequent replacements are a running cost; a large one-off tool order can go through AIA |
| Diagnostic equipment | OBD scanners, code readers, oscilloscopes, software subscriptions | Often the biggest single tool spend; claim via AIA in the year bought |
| Larger equipment | Trolley jacks, axle stands, engine hoist, transmission jack, compressor | Capital items, normally claimed in full under AIA |
| Van running costs | Fuel, insurance, servicing, MOT, road tax, repairs, breakdown cover | Claim actual costs (keep receipts) OR the flat mileage rate, never both |
| Mileage between jobs | 45p per mile first 10,000 miles, 25p above | Only if using the simplified method instead of actual costs |
| Public liability and motor trade insurance | Annual premiums, including road-risk cover for moving customer vehicles | Fully deductible; motor trade insurance is essential and legitimate |
| Work clothing and PPE | Overalls, safety boots, mechanic's gloves, eye protection | Protective gear and branded uniform only, not ordinary clothes |
| Phone, booking and invoicing | Business proportion of mobile, scheduling apps, card-reader fees | Apportion if the phone is also personal |
| Advertising and listings | Google Business, local ads, vehicle livery, Checkatrade-style platforms | Fully deductible |
| Trade subscriptions and training | Technical data subscriptions (such as wiring diagrams), refresher courses | Allowable if updating existing skills, not training into a new trade |
| Accounting software | TapTax and similar | Fully deductible |
The single most common HMRC challenge for mechanics is the dual-use vehicle and dual-use tools. If you use your van at weekends for the family, you cannot claim 100% of its costs under the actual method; you apportion to the business percentage. The same applies to a phone you also use personally. Keep the apportionment realistic and documented, because a 100% business claim on something you obviously also use privately is a red flag.
Here is the issue that catches more mobile mechanics than any other. You buy a part at the trade counter for GBP 200, fit it, and charge the customer GBP 280 plus GBP 90 labour, so they pay GBP 370. For VAT-threshold purposes your turnover on that job is the full GBP 370, not the GBP 90 of labour. The parts are not netted off; the gross invoice is your turnover.
That matters because the VAT registration threshold is GBP 90,000 of taxable turnover in any rolling 12-month window, not the tax year. A mechanic doing big-ticket jobs (clutches, timing chains, turbos) where parts dominate the invoice can sail past GBP 90,000 on turnover while the labour element is modest. Once you breach the threshold you have 30 days to register, and missing that carries penalties. You can sense-check where you stand with the VAT calculator.
If you do register, you charge 20% VAT on your invoices, but you also reclaim the VAT you paid on the parts and on most of your overheads. Because the bulk of a mechanic's parts purchases already carry input VAT you can recover, registration is less painful than it looks for a parts-heavy business. The pain falls mainly on private customers who cannot reclaim the VAT you add. Many mechanics serving only private motorists therefore manage turnover carefully to stay below the threshold; those doing fleet, trade or business work, whose customers can reclaim, sometimes register voluntarily to recover input tax.
Take a busy mobile mechanic invoicing GBP 55,000 across a year (labour plus parts charged on), running a well-used van and replacing tools through the year.
| Amount | |
|---|---|
| Gross turnover (labour + parts) | GBP 55,000 |
| Less: parts re-charged to customers (cost of sales) | GBP 18,000 |
| Less: van actual running costs (business proportion) | GBP 6,500 |
| Less: tools and consumables | GBP 2,400 |
| Less: diagnostic software subscriptions | GBP 600 |
| Less: motor trade and public liability insurance | GBP 1,400 |
| Less: phone, booking and card fees | GBP 700 |
| Less: PPE and workwear | GBP 300 |
| Less: advertising and livery | GBP 500 |
| Taxable profit | GBP 24,600 |
| Personal allowance | GBP 12,570 |
| Taxable income | GBP 12,030 |
| Income Tax at 20% | GBP 2,406 |
| Class 4 NIC at 6% on profit above GBP 12,570 | GBP 721.80 |
| Total tax and NIC due | GBP 3,127.80 |
Notice that turnover was GBP 55,000 but profit was under GBP 25,000, because parts re-charged at near cost and a heavily worked van strip out most of the headline figure. That GBP 55,000 turnover is also worth watching: it is comfortably inside the GBP 90,000 VAT threshold here, but a mechanic taking on a few more high-parts jobs each month could cross it, which is the moment VAT registration becomes compulsory.
The mistake parts-heavy mechanics make is watching their labour income and assuming they are nowhere near VAT registration. HMRC counts the full invoice, parts included, so a clutch-and-cambelt specialist can hit £90,000 of turnover while taking home a far smaller profit.
Making Tax Digital for Income Tax (MTD for IT) replaces the single annual Self Assessment return for most sole traders with quarterly digital updates and a final year-end declaration. The timetable is:
A mobile mechanic clearing GBP 50,000 of profit, or close to it, should have MTD-compatible software in place before April 2026. The practical benefit for a trade with constant small purchases and per-job parts is real: software like TapTax captures each part, each job and each business mile as it happens, so you always know your running tax position rather than reconstructing a shoebox of receipts in January. The full MTD for sole traders guide walks through exactly what the quarterly updates involve and which deadlines replace the old single filing date.
Even below the threshold, recording digitally now means that when you do cross GBP 30,000 or GBP 50,000, you simply continue rather than scramble to change how you work.
Netting parts off turnover for the VAT test. This is the costliest error. Your VAT turnover is the gross invoice including parts. A mechanic who only watches labour income can blow through GBP 90,000 unregistered and face penalties plus backdated VAT.
Claiming 100% of a dual-use van or phone. If the van does the school run at weekends, the claim must be apportioned. An obviously personal-use asset claimed at 100% invites an enquiry.
Switching the van method mid-stream. You must keep the same method (mileage or actual cost) for the life of each vehicle. Deciding the flat rate suited you last year but actual costs suit you this year, on the same van, is not allowed.
Forgetting big tool and diagnostic purchases. A GBP 1,500 diagnostic scanner is fully deductible in the year you buy it through the AIA. Mechanics routinely forget to claim large kit because it feels like an asset rather than an expense.
Missing payments on account. If your January bill tops GBP 1,000, HMRC will add payments on account: 50% towards next year in January and another 50% in July. First full year of decent profit can therefore mean roughly one and a half years of tax landing at once. Set money aside for it.
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