Mobile mechanics can charge for diagnostics. Agree the fee before you start, put it on the invoice as its own line, and say clearly whether it is deducted if the customer goes ahead with the repair. That avoids most disputes.
*By Kamal Leadbitter, Founder. Last reviewed October 2026.*
Should mobile mechanics charge for diagnostics?
Yes. Finding the fault takes time, equipment and skill. Most customers accept a diagnostic charge when it is agreed upfront rather than added afterwards.
Should diagnostics appear separately on an invoice?
Yes. A separate line such as "Diagnostic check — engine warning light £45" shows exactly what was done, keeps it apart from parts and labour, and makes your pricing easy to follow.
What if the customer declines the repair?
Invoice the diagnostic fee on its own. Note what you found so the customer has something for their money, for example "Fault code P0301 — cylinder 1 misfire; coil pack recommended".
How should a diagnostic charge be worded?
Keep it plain: what you checked, the result and the price. If the fee is deducted from the repair, show the deduction as a separate negative line so the customer can see it.
How do you avoid disputes over diagnostic fees?
- Quote the fee before you plug in
- Say whether it is deducted from repair work
- Record what you found in writing
- Invoice the same day, while the details are fresh
Example voice note
"Invoice James Turner, diagnostic check £45, misfire on cylinder 1, coil pack recommended." SaidToPaid turns that into an invoice draft with the diagnostic on its own line, ready for you to check and send.
Related: Mobile mechanic invoicing software · Mobile mechanic invoice template UK · How voice invoicing works for mechanics
Try it with your numbers
Labour rate calculator
Put in your own monthly costs and the hours you can actually bill. Parts are charged separately.
- Break-even rate (costs only)
- £8.04/hr
- Rate to hit your take-home
- £33.90/hr
- Billable hours per month
- 108
A starting point worked out from your figures only. Nothing is saved. Excludes VAT.
Use these prices on a free invoiceInvoice terms you can copy
Plain wording to add to the notes on your invoices. Save it once in your settings and it goes on every invoice. General guidance, not legal advice.
Late payment (business customers)
Payment is due within 30 days of the invoice date. If you are a business customer, we may charge interest on late payment at 8% a year above the Bank of England base rate, plus fixed compensation, under the Late Payment of Commercial Debts (Interest) Act 1998.
Parts warranty
Parts supplied carry the manufacturer's warranty only. Customer-supplied parts are fitted at the customer's risk and are not covered for labour if they fail.
Diagnostics
Diagnostic time is charged even if the customer chooses not to go ahead with the repair.
Waste disposal
A disposal charge applies for used oil, filters, batteries and other waste removed from the vehicle.
The late payment law only covers business-to-business invoices. Fixed compensation is £40 on debts under £1,000, £70 up to £9,999.99 and £100 from £10,000.
Mobile mechanic checklist (UK)
- Register for VAT once your taxable turnover passes the current threshold (£90,000 from April 2024). Below that, don't add VAT to invoices.
- Waste oil, filters and batteries are hazardous waste. Use a registered waste carrier and keep the paperwork.
- Have public liability and motor trade or road risks insurance that covers working on customers' cars.
- Record the vehicle registration and mileage on every invoice. It helps the customer's service history and settles disputes.
- Keep invoices and records for at least 5 years after the 31 January Self Assessment deadline.
General guidance, checked October 2026. Rules change and vary by council, so check with your local authority, insurer or HMRC.
From individual Trustpilot reviews
A customer's experience
“I can speak the job details into SaidToPaid, check the invoice draft and send it to the customer. It’s been really useful when I’m working away from a desk.”