Tax & Expenses

How to Track Expenses as a Self Employed Builder UK 2026

Updated July 2026 · 7 min read · BuilderLog Team

The simplest habit that saves the most money at tax time isn’t complicated — it’s just rarely done consistently. Here’s a system that takes under a minute per job.

Why most builders underclaim

It’s not laziness. It’s the gap between spending money and recording it. You buy materials at the merchant, pay for a skip, fill up with diesel, pay for parking — and by the time you get home, recording it feels like admin you don’t have time for. So you don’t. And at tax time, you’re guessing.

The average self employed builder has £7,000–£12,000 in legitimate claimable expenses per year. Most claim £4,000–£6,000 because they lost receipts, forgot journeys, or didn’t realise something was claimable. That gap costs them £600–£1,200 in unnecessary tax.

The 30-second habit

When you finish a job for the day — sitting in the van, waiting for the kettle, whatever — open BuilderLog and log what you spent:

• Materials you bought
• Miles you drove
• Skip hire or waste disposal
• Parking
• Any other cost

That’s it. Thirty seconds, once a day. Over a year, this habit is worth hundreds in tax savings because every expense reduces your taxable profit.

What to track

Category	Examples	Typical annual total
Materials	Cement, timber, bricks, fixings	£2,000–£5,000
Mileage	55p/mile for all business journeys	£3,000–£5,500
Skip hire	Skip per job, tip runs	£1,000–£3,000
Scaffolding	Hired per job	£500–£2,000
Tools	Replacements, new equipment	£500–£2,000
Insurance	Public liability, tool cover	£400–£800
CSCS + training	Card renewal, courses	£200–£500

Job costs vs business expenses

Some expenses are tied to specific jobs (materials for a kitchen extension, skip for a demolition). Log these against the job in BuilderLog — this shows your real profit per job.

Other expenses aren’t tied to any job (annual insurance, CSCS renewal, new drill). Log these as Business Expenses on the Report page. Both types reduce your taxable profit and appear on your tax report.

Digital vs paper

From April 2026, Making Tax Digital requires digital records for builders earning over £50,000. But even below that threshold, digital is better: you can’t lose a phone app, you can’t smudge a digital entry, and you can search and total your records instantly.

The receipt problem

Paper receipts fade, get lost, go through the wash, and end up in a pile you never sort. The solution isn’t to be more careful with receipts — it’s to record the expense digitally the moment you incur it and stop relying on paper.

Take a photo of the receipt if you want a backup, but the primary record should be digital: the amount, the category, the date, and what it was for. That’s what HMRC actually needs — not a faded thermal print from Screwfix.

Mileage — the most valuable habit

Mileage is the single most valuable expense to track consistently because the amounts are large and there’s no receipt to keep — it’s purely a log. A builder driving 10,000 business miles at 55p/mile claims £5,500 off their taxable profit. At 20% tax, that’s £1,100 saved.

But without a contemporaneous log, you can’t claim any of it. HMRC will reject a retrospective estimate. You need: date, from, to, purpose, miles — recorded at or near the time of the journey.

BuilderLog makes this automatic. When you add mileage as a cost against a job, it records the date, the job (which gives you the purpose), and the distance. The claimable amount is calculated at 55p/mile automatically.

End of year — what good tracking gives you

When January arrives and it’s time to file your self assessment, a builder who tracked throughout the year opens BuilderLog, taps Report, selects the tax year, and sees:

• Total income
• Total costs broken down by category (materials, mileage, skip hire, scaffolding, tools, insurance…)
• Business expenses not tied to specific jobs (CSCS, training, phone)
• Net profit
• Estimated tax

Enter these figures into your self assessment. Twenty minutes and you’re done. Compare that with the builder who spent January trying to reconstruct 12 months of expenses from bank statements and half-remembered receipts.