CIS Tax Return 2026: How Construction Subcontractors Claim Back Overpaid Tax

A complete guide for UK construction subcontractors: how CIS deductions work, why most subcontractors overpay tax, how to claim your refund through Self Assessment, and what the April 2026 CIS rule changes mean for your compliance.

If you work in construction as a self-employed subcontractor, your contractor deducts 20% from your pay each month and sends it to HMRC before you ever see it. The assumption many subcontractors make is that this covers their tax. It does not.

Those CIS deductions are advance payments towards your income tax and National Insurance bill — not the final calculation. For most subcontractors, the amount deducted through CIS significantly exceeds the actual tax owed, particularly once allowable expenses are factored in. Claiming that overpayment back requires filing a Self Assessment tax return, and doing it correctly is the difference between a meaningful refund and leaving money with HMRC.

How CIS Deductions Work

The Construction Industry Scheme (CIS) requires contractors to deduct tax from payments to subcontractors before those payments arrive in your account. The deduction rate depends on your registration status:

Status	CIS Deduction Rate	Who Qualifies
Registered subcontractor	20% on labour element	Registered with HMRC under CIS
Unregistered subcontractor	30% on labour element	Not registered with HMRC
Gross Payment Status	0% — full payment received	Meets HMRC qualifying conditions

The deduction is calculated on the labour element only. Materials, tool hire, and direct costs you pass on to the contractor are excluded from the CIS deduction calculation. Your contractor must give you a Payment and Deduction Statement each month showing what was paid and what was deducted. Keep every statement — they are the evidence supporting your refund claim.

Why Most CIS Subcontractors Are Owed a Refund

A CIS deduction of 20% is calculated on your gross labour income before any expenses are considered. Your actual tax liability is based on your profit — income minus allowable expenses — not your gross income. For most subcontractors with legitimate business costs, the CIS deduction significantly overshoots the tax actually owed.

Worked Example: Self-Employed Electrician

Item	Amount
Gross CIS income earned	£45,000
CIS deducted by contractor (20%)	£9,000
Allowable business expenses (van, tools, insurance, phone)	£7,500
Taxable profit (£45,000 – £7,500)	£37,500
Taxable income after personal allowance (£37,500 – £12,570)	£24,930
Income tax at 20%	£4,986
Class 4 NIC (approx)	~£2,100
Total tax liability	~£7,086
Already paid via CIS deductions	£9,000
Refund due	~£1,914

This is a conservative example. Subcontractors with higher tool, van, materials, or accommodation costs will have a larger refund. Those unaware of all legitimate claimable expenses routinely leave hundreds or thousands of pounds with HMRC unnecessarily.

Allowable Expenses for CIS Subcontractors

The key to maximising your CIS refund is claiming every allowable expense correctly. HMRC allows deductions for costs that are wholly and exclusively for business purposes.

Van and Vehicle Costs

If you use a vehicle exclusively for work, claim the running costs including fuel, insurance, servicing, road tax, and MOT. For mixed business and personal use, claim the business proportion only. Alternatively, use HMRC’s flat rate mileage allowance: 45p per mile for the first 10,000 miles, 25p beyond. For lower-mileage users, the flat rate often produces a higher deduction than actual costs.

Tools and Equipment

Hand tools, power tools, safety equipment, and specialist equipment are all deductible in the year of purchase for most sole traders using the Annual Investment Allowance. Keep all receipts.

Protective Clothing and Workwear

Specialist workwear, boots, hard hats, high-visibility vests, and safety gloves are allowable. Generic clothing that could reasonably be worn outside work is not deductible.

Insurance, Phone, Training, and Accommodation

Business insurance premiums are fully deductible. The business proportion of your phone bill is claimable. Training costs that maintain or update existing skills qualify — CSCS card renewals, first aid, and similar certifications are included. If work requires you to stay away from home overnight, reasonable accommodation and meal costs can be claimed under HMRC’s temporary workplace rules.

Accountancy Fees

The cost of having your CIS Self Assessment return prepared and filed by an accountant is itself an allowable business expense — meaning it effectively pays for itself through the tax saving it generates.

How to File Your CIS Self Assessment Return

Your 2025/26 tax return covers income earned between 6 April 2025 and 5 April 2026. The online filing deadline is 31 January 2027. Missing this triggers an automatic £100 penalty, escalating to further charges at 3 months, 6 months, and 12 months.

1. Register for Self Assessment if not already registered. HMRC requires registration by 5 October 2026 for the 2025/26 tax year if you are new to Self Assessment. Register online via gov.uk.
2. Gather all CIS Payment and Deduction Statements from every contractor you worked for during the year.
3. Total your gross CIS income — this is the full amount invoiced for labour, before deductions. Do not use the amount received after deductions.
4. Calculate your allowable expenses — use the categories above and retain all supporting receipts.
5. Complete the SA103F self-employment pages. Enter your CIS deductions in Box 81. This tells HMRC the advance payments already made on your behalf.
6. Submit and wait. If CIS deductions exceed your liability, HMRC issues a refund. Repayment is typically processed within four to six weeks of submission.

CIS Changes From April 2026: What Subcontractors Need to Know

The biggest CIS reforms in twenty years took effect on 6 April 2026, following a government consultation that closed in February 2026. As the HMRC CIS 340 guidance confirms, these changes introduce new obligations for contractors and new risks for subcontractors with Gross Payment Status.

1. Nil Returns Are Back for Contractors

Contractors who do not pay any subcontractors during a tax month must now either file a nil CIS return by the 19th of the following month, or notify HMRC in advance. This was removed in 2015 and has been reinstated from April 2026. As a subcontractor, this matters if you also occasionally act as a contractor — and if your main contractors have gaps in their return filing history that could affect your payment and deduction statements.

2. New Fraud Liability Powers — Supply Chain Risk

Under sections 62A and 62B of the Finance Act 2026, HMRC can now pursue any business connected to a fraudulent CIS supply chain — even if that business was not directly involved in the fraud. For legitimate subcontractors who occasionally hire other tradespeople, this means you need a basic documented due diligence process: verify CIS status, check Companies House for director information, and keep a dated record of your checks.

3. Gross Payment Status — Reapplication Period Extended to Five Years

If HMRC cancels your Gross Payment Status, the reapplication period has increased from one year to five years. For subcontractors who rely on GPS for cash flow, the consequences of losing it are now far more severe. Any late Self Assessment filing, outstanding VAT return, or PAYE liability now carries a significantly higher practical risk than in previous years. Maintain a clean compliance record as a priority.

Gross Payment Status: Is It Worth Applying For?

If your CIS deductions consistently exceed your tax liability, Gross Payment Status is worth considering. Under GPS, contractors pay you the full invoice amount — no CIS deduction — and you pay the correct amount of tax via Self Assessment at year-end.

The cash flow benefit is significant. Instead of waiting until January to reclaim overpaid tax, you hold the cash throughout the year. To qualify, HMRC requires that your tax and NI obligations are fully up to date, your business carries out construction work in the UK, and you meet the turnover thresholds for the preceding 12 months (£30,000 for sole traders). HMRC reviews GPS compliance annually.

How a CIS Accountant Can Help

The most common mistake CIS subcontractors make is underestimating allowable expenses and paying more tax than necessary. The second is not registering for Self Assessment at all and never reclaiming CIS deductions — effectively making an interest-free gift to HMRC year after year.

Our CIS Returns service covers everything: registration, expense calculation, Self Assessment filing, GPS applications, and HMRC correspondence. For subcontractors based in London, Wimbledon, South West London, and across the UK, we provide a fixed-fee CIS return service with no hidden charges. Most new clients find their first professionally prepared CIS return produces a refund that comfortably exceeds the cost of the service.

Frequently Asked Questions

Do I have to file a Self Assessment return if I am a CIS subcontractor?

Yes. Even if your contractor deducts CIS tax from every payment, you are still required to file a Self Assessment tax return each year. The CIS deductions are advance payments towards your final tax liability, not a substitute for filing. From 2026/27, those mandated under MTD for Income Tax (sole traders and landlords earning above £50,000) will file quarterly updates instead of an annual return — but the obligation to report remains.

What happens if my CIS deductions are more than my tax bill?

HMRC issues a tax refund for the difference. Once your Self Assessment return is processed and the deductions verified against the returns submitted by your contractors, the overpayment is repaid — usually within four to six weeks. Make sure you provide accurate bank details to HMRC for the repayment.

Can I reclaim CIS deductions if I operate through a limited company?

Yes, but the process differs. For a limited company, CIS deductions suffered are offset against the company’s PAYE/NIC or CIS liabilities rather than through Self Assessment. The company reports the deductions on its Employer Payment Summary submissions. Any excess after offsetting can be reclaimed as a cash repayment. The interaction between CIS, company PAYE, and potentially off-payroll working rules is complex — professional advice is recommended.

What is the deadline for registering as a CIS subcontractor?

There is no specific deadline for CIS subcontractor registration — you can register online with HMRC at any time. However, until you are registered, contractors must deduct 30% rather than 20% from your payments. Registering immediately when you start construction work as self-employed saves you 10 percentage points on every payment received while unregistered.

How far back can I claim a CIS refund?

You can claim a CIS refund for the previous four tax years by filing late Self Assessment returns. HMRC imposes automatic late filing penalties, but these may be mitigated by a reasonable excuse application in some circumstances. Our CIS Returns team regularly files returns for clients covering multiple prior years to recover overpaid tax going back as far as the allowable four-year window.