CIS Tax Refund Explained: How UK Subcontractors Get £1,000+ Back

UK construction subcontractors taxed under the Construction Industry Scheme (CIS) almost always overpay tax during the year. The 20% standard deduction (or 30% unmatched rate) is taken from your gross labour at source by your contractor - but it ignores your Personal Allowance, your business expenses, and the materials you supplied. Reconciling that at year-end through Self Assessment is how the typical CIS subcontractor recovers between £1,000 and £4,000 a year.

This guide explains exactly how the refund works, when an accountant is worth their fee, and when you can do it yourself for free.

How CIS deductions work

Under the Construction Industry Scheme, contractors must deduct tax from payments to subcontractors and pay it to HMRC. The deduction rate is:

• 20% standard rate - if your UTR matches HMRC's CIS database when the contractor verifies you.
• 30% unmatched rate - if HMRC cannot verify your UTR (typically because you haven't registered, or you're using the wrong UTR).
• 0% gross payment status - if you've applied for and been granted gross payment, usually because you have a substantial trading history and meet the turnover threshold.

The deduction comes off your labour element only. Materials you supplied at cost, plant hire, fuel for plant, and similar pass-through costs should be excluded from the deduction calculation - but only if your contractor knows about them and shows them on the CIS payment and deduction statement.

Why you almost certainly overpaid

Three structural reasons:

1. Your Personal Allowance was ignored. You have £12,570 of tax-free income in 2026/27. CIS deduction of 20% on the first £12,570 of your annual labour is £2,514 - and that's before any expenses. You should be reclaiming that as the first line of your refund.
2. Your expenses were ignored. Tools, protective equipment, professional subscriptions, training, your van or its mileage, your work phone, the home-office portion of your bills if you do paperwork from home - all reduce your taxable profit. None of them are visible to your contractor.
3. Your materials were sometimes wrong. If your contractor deducted 20% from a payment that included materials you supplied at cost, you've been over-deducted on a chunk that wasn't even taxable in the first place.

How the refund actually works

You do it through Self Assessment, not through PAYE. The Self Assessment cycle:

1. Register as self-employed with HMRC (free, online at gov.uk/log-in-file-self-assessment-tax-return/register-if-youre-self-employed). You only do this once.
2. Keep your CIS payment and deduction statements (your contractor must give you one for every payment, every month).
3. After 5 April each year, file a Self Assessment return covering the tax year that just ended. The deadline is 31 January for online filing.
4. Declare your gross labour income, your CIS deductions taken, your business expenses, and your materials. HMRC works out your tax liability and offsets the CIS deductions you've already paid.
5. The difference is your refund. HMRC pays it directly into your bank account, usually within 4-8 weeks of filing.

You do not need to wait until 31 January. File as soon as you have all your statements after 5 April; the earlier you file, the earlier you're refunded.

A worked example

Tom is a CIS-registered electrician. In 2025/26 he earned £45,000 gross labour from contractors, with £9,000 deducted at the 20% standard rate. His allowable expenses for the year:

• Tools and small plant: £1,800
• Van fuel and maintenance (business proportion): £4,200
• Mobile phone (business proportion): £480
• Public liability insurance: £350
• Professional body subscription: £180
• Training course: £600
• Home-office allowance (£6/week × 52): £312

Total expenses: £7,922.

His Self Assessment calculation:

Gross labour income:                  £45,000.00
Less allowable expenses:              -£7,922.00
Taxable profit:                       £37,078.00
Less Personal Allowance:             -£12,570.00
Income subject to tax:                £24,508.00

Income tax at 20%:                     £4,901.60
Class 2 NI (£3.45/wk × 52):              £179.40
Class 4 NI on profit above £12,570:    £1,961.04
                                       (£24,508 × 8%)
Total tax + NI owed:                   £7,042.04

Less CIS deductions already taken:    -£9,000.00
                                      ──────────
REFUND:                                £1,957.96

Tom is owed roughly £1,958. Without claiming his expenses, his refund would have been only £358 - the expenses are doing the bulk of the work.

When to use an accountant

Honest answer: you can do simple CIS Self Assessment yourself for free using HMRC's online filing. The HMRC system walks you through it and the maths is automated.

A specialist CIS accountant or refund firm is worth their fee when:

• You have multiple years' worth of unfiled returns (penalties stack quickly; a specialist negotiates them).
• Your expenses are complex or partially documented (fuel without all receipts, partial home office, mixed personal/business van use).
• You have mixed income - PAYE plus CIS in the same year, or self-employment alongside.
• You disagree with HMRC about a previous calculation and need representation.
• You want to apply for gross payment status and need help with the turnover and compliance tests.

A specialist refund firm typically charges 20-35% of your refund. For Tom's £1,958 refund above, a 25% fee would be £490 - useful if his time is worth more than £490 and the paperwork is daunting; expensive if his return is straightforward and he could handle it himself in a Sunday afternoon.

Common mistakes to avoid

1. Not registering as self-employed. If HMRC has no record of you as self-employed, you can't file Self Assessment and you can't recover anything. Registration is free and takes ten minutes.
2. Throwing away your CIS statements. You must keep them for at least six years. HMRC can ask for them at any point. A simple folder by tax year is enough.
3. Not claiming expenses you're entitled to. Tools, fuel, training, professional fees - all reduce your taxable profit. Take the time.
4. Missing the 31 January deadline. Late-filing penalty is £100 the day after, plus £10/day from three months after, plus 5% of unpaid tax at six months. Costly.
5. Using a refund firm without reading the contract. Some firms charge ongoing percentages, not one-off fees. Read the small print before signing.

Disclaimer

PayslipIQ provides automated educational guidance based on the figures you supply. It is not regulated tax advice or accountancy advice. CIS Self Assessment can be straightforward, but if your situation is complex (multi-year returns, contested HMRC determinations, gross-payment-status applications) please use a CTA-qualified tax adviser or an ICAEW/ACCA-registered accountant.