Common CIS Mistakes & How to Avoid Them (UK Contractor Guide)

Working under the Construction Industry Scheme (CIS) can feel overwhelming. Between deductions, invoices, missing statements and HMRC rules, it’s easy to make small mistakes that cost you money.

The good news?
Most of these issues are simple to fix — once you know what to look for.

Below are the most common CIS mistakes UK subcontractors make, plus exactly how to avoid them so you’re paid correctly and receive every penny of the refund you’re entitled to.

1. Not Keeping Your CIS Statements

Your CIS statements show exactly how much tax your contractor deducted before paying you.
If you lose them, it becomes harder to:

  • Claim your refund

  • File your tax return correctly

  • Prove your deductions to HMRC

How to avoid this mistake

Ask your contractor to email or text your CIS statement every time you’re paid.
If you’re missing any, don’t worry — I can contact the contractor on your behalf and retrieve them.

2. Not Claiming All Allowable Expenses

One of the biggest ways subcontractors lose money is by not claiming everything they’re entitled to.

You can claim for:

  • Tools

  • Materials

  • Workwear & PPE

  • Fuel or mileage

  • Home office use

  • Mobile phone

  • Courses & training

  • Accountant fees

Claiming every eligible business expense reduces your tax bill and often leads to a larger CIS tax refund.

3. Mixing Personal and Business Money

Putting all your income and spending into one personal account makes bookkeeping confusing and increases the risk of errors.

How to avoid this mistake

Use one separate account for business income and expenses.
It doesn’t need to be an official “business account” — just keep it separate for clarity and easier tax returns.

4. Not Tracking Your Mileage

Thousands of subcontractors miss out on money because they forget to track mileage.

HMRC allows you to claim:

  • 45p per mile for the first 10,000 miles

  • 25p per mile after 10,000

Failing to log your mileage means missing out on potential tax savings worth hundreds — sometimes thousands.

5. Forgetting to Claim for Tools & Equipment

Your tools aren’t just work essentials — they’re tax-deductible business expenses.

You can claim for:

  • New tools

  • Repairs

  • Replacements

  • Upgrades

  • Van tools

If you’ve bought equipment this year, make sure it goes on your expenses.

6. Filing Your Return Late

Late filing can lead to:

  • Penalties

  • Delayed refunds

  • HMRC letters and fines

  • Unnecessary stress

If you’re behind, I can get you caught up quickly — whether you’re a few months or several years overdue.

7. Misunderstanding How CIS Refunds Work

Many subcontractors believe their contractor “pays their tax for them.”

That isn’t exactly how CIS works.

CIS deductions are advance tax payments, but you still need:

  • A completed tax return

  • A proper list of expenses

  • All CIS deduction statements

This is the only way HMRC can calculate what you’re owed — and issue your refund.

8. Trying to Figure It Out Alone

CIS rules can be confusing — and you don’t have to do everything yourself.

I help subcontractors with:

  • CIS refunds

  • Missing CIS statements

  • Bookkeeping

  • Tax returns

  • HMRC letters

  • Multi-year backlogs

I take the stress off your shoulders so you can focus on your work.

Need Help With Your CIS Refund or Tax Return?

If you need support with:

✔ CIS refunds
✔ Missing statements
✔ Filing your tax return
✔ Organising your accounts
✔ Understanding your expenses

Just send me a message — I’ll make everything clear, simple, and stress-free.

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