CIS Tax Refund: How to Claim Back What HMRC Owes You (2026 Guide)

Published: 14 March 2026 | Reading time: 8 minutes

If you work in construction as a self-employed subcontractor under the Construction Industry Scheme (CIS), your contractor deducts 20% (or 30% if you're unregistered) from every payment. That money goes straight to HMRC as a kind of advance tax payment.

The thing is — most CIS subcontractors overpay. When you file your Self Assessment tax return and claim your allowable expenses, your actual tax bill is usually lower than all those deductions added together. The difference? HMRC owes it back to you.

This guide walks you through exactly how to claim your CIS tax refund — what to gather, where to go, how long it takes, and how to make sure you're not leaving money on the table.

Why CIS Subcontractors Usually Get a Refund

The maths is straightforward. Your contractor deducts 20% of your gross payment — but your actual tax liability is almost always less than 20% of gross income, because:

• You have a Personal Allowance — £12,570 in 2025/26, meaning the first £12,570 of profit is tax-free
• You have allowable expenses — tools, materials, fuel, workwear, van costs, phone bills, and more all reduce your taxable profit
• The 20% rate exceeds your marginal rate on lower earnings — if your taxable profit is under £50,270, you pay 20% income tax, but that's on profit after expenses, not gross income
• National Insurance isn't covered — the CIS deduction doesn't account for NI correctly across all earnings levels

Example: Say you earned £40,000 gross under CIS. Your contractor deducted £8,000 (20%). But after £6,000 in legitimate expenses, your taxable profit is £34,000. After your Personal Allowance, you're taxed on £21,430 — meaning your income tax bill is roughly £4,286. HMRC owes you back £3,714.

Many CIS subcontractors never claim this because they don't file a Self Assessment. Don't be one of them.

Step-by-Step: How to Claim Your CIS Tax Refund

Step 1: Register for Self Assessment (if you haven't already)

CIS refunds come through Self Assessment — there's no separate "CIS refund form" for sole traders. If you're not registered, go to GOV.UK and register as self-employed. You'll need your National Insurance number and the start date of your self-employment.

HMRC will post you a Unique Taxpayer Reference (UTR) within 10 working days. You'll need this to file your return.

Deadline to register: 5 October after the end of the tax year you want to claim for. Miss this and you risk penalties on top of everything else.

Step 2: Gather Your CIS Statements

Every contractor who paid you under CIS must give you a CIS deduction statement showing:

• The gross amount paid
• The cost of materials (excluded from deduction)
• The deduction rate applied (20% or 30%)
• The amount deducted
• The net amount paid to you

Contractors are supposed to provide these monthly. If yours didn't, ask for them — they're legally required to provide them. You need the totals for the full tax year (6 April to 5 April).

Add up all deductions across all contractors. This is the total that HMRC has received on your behalf.

Step 3: Compile Your Allowable Expenses

This is where most CIS subcontractors leave money on the table. You can deduct any expense that is "wholly and exclusively" for business purposes. Common allowable expenses include:

• Tools and equipment — power tools, hand tools, safety gear
• Vehicle costs — fuel, insurance, servicing, MOT (van used for work)
• Materials — anything you bought that wasn't billed directly to contractors
• Protective clothing — boots, hi-vis, hard hats, gloves
• Mobile phone — business calls portion
• Accountant fees — yes, the cost of getting your tax sorted is tax-deductible
• Training — courses related to your trade (CSCS card renewals, etc.)
• Business insurance — public liability, tools insurance

Keep receipts. HMRC can ask for evidence up to four years after the return is filed.

Step 4: File Your Self Assessment Tax Return

You can file online at GOV.UK or use third-party tax software. When completing your return:

1. Enter your total gross CIS income (before deductions) in the self-employment section
2. Enter your allowable expenses
3. In the "Other tax reliefs" section, enter the total CIS deductions made by your contractors
4. The return will calculate your final tax liability and offset the CIS deductions already paid
5. If deductions exceed your liability, the surplus becomes your refund

The Self Assessment deadline for online returns is 31 January following the end of the tax year. For 2024/25 (tax year ending 5 April 2025), that deadline is 31 January 2026 — which has already passed. If you missed it, file now anyway — the refund is still yours, but you may owe a late filing penalty.

Step 5: Request Payment of Your Refund

Once you've filed, HMRC will process your return and calculate what they owe you. You can:

• Receive a bank transfer — log in to your HMRC online account, go to "Repayment" and enter your bank details. This is the fastest option.
• Receive a cheque — HMRC will post it to your address on record if no bank details are provided

You'll normally see a repayment within 5 working days if you've provided bank details. Cheques can take 2–3 weeks.

How Far Back Can You Claim?

You can reclaim overpaid CIS tax going back four tax years. In March 2026, that means you can still claim for:

• 2024/25 (deadline 31 Jan 2026 — may be late, but still claimable)
• 2023/24
• 2022/23
• 2021/22

If you've never filed a Self Assessment despite working under CIS for years, you could be owed a significant sum. Some CIS subcontractors reclaim £3,000–£8,000 once they file properly for multiple years.

Beyond four years, the claim is time-barred — HMRC won't pay it regardless of the overpayment.

Common Mistakes That Delay or Reduce Your CIS Refund

Forgetting to enter CIS deductions on the return

It sounds obvious, but this is surprisingly common — especially when using a generic accountant who's not CIS-familiar. If CIS deductions aren't entered as a tax credit, you'll calculate as if you owe the full amount, not as if HMRC already has some of it.

Using gross income instead of profit

You pay tax on profit (income minus expenses), not gross income. If your accountant or tax software isn't properly accounting for your expenses, your tax calculation will be wrong and your refund will be lower than it should be.

Missing CIS statements from one contractor

If you worked for three contractors but only have two CIS statements, you're missing deductions from your calculation. Chase every contractor — the statement shows deductions made in your name, which are legally yours to reclaim.

Outdated bank details on HMRC account

HMRC will try to pay by bank transfer to the account on file. If you've changed accounts and not updated HMRC, they'll send a cheque to your address — and if that's changed too, it can go missing. Keep your details current via your Personal Tax Account on GOV.UK.

Not claiming materials as expenses

Under CIS, contractors are supposed to exclude material costs from the deduction calculation. But many subcontractors supply materials and don't track this separately. If you bought £4,000 of materials and your contractor didn't exclude this from the deduction calculation, you may have been overdeducted — this should show up in your CIS statements, but always check.

What About Limited Company CIS Subcontractors?

If you operate as a limited company (not a sole trader), the refund process is different. Your company can offset CIS deductions against its PAYE liabilities — essentially paying less to HMRC each month until the deductions are used up. If deductions exceed PAYE obligations, the company can apply for a refund using form CIS132.

This is separate from your personal Self Assessment. If you're a director drawing a salary, your company handles CIS refunds; you handle personal income tax separately.

Should You Use a Tax Agent?

Many CIS subcontractors use tax agents or accountants who specialise in construction. They typically charge £150–£300 to file a CIS Self Assessment return, but often find additional expenses you'd have missed — more than covering their fee.

Be cautious of "tax refund companies" that charge 30–40% of your refund as commission. For a £2,000 refund, that's £800 in fees. A flat-fee accountant is almost always better value.

That said, the process genuinely isn't complicated if you're organised. With the right templates and a clear checklist, most CIS subcontractors can file their own Self Assessment confidently.

Quick Summary: Your CIS Refund Checklist

• ✅ Register for Self Assessment (UTR required)
• ✅ Collect CIS statements from every contractor you worked for
• ✅ Add up all deductions across all contractors
• ✅ Compile all allowable business expenses with receipts
• ✅ File your Self Assessment online — enter gross CIS income, expenses, and CIS deductions
• ✅ Update bank details on your HMRC Personal Tax Account
• ✅ Check for prior years — you can go back four tax years
• ✅ Chase HMRC if no refund after 8 weeks

CIS refunds aren't a loophole or a grey area — they're simply what happens when you've overpaid tax at source and file a proper return. Most construction subcontractors are owed something. Get organised, file your return, and get your money back.

This guide covers the 2025/26 tax year. Tax rules and thresholds are subject to change — always check the latest GOV.UK guidance or speak to a qualified tax adviser for your specific circumstances.