CIS Tax Refund Calculator.
Most construction subcontractors overpay tax through the CIS scheme and are owed a refund each year. Enter your figures below to estimate yours in seconds.
Your figures
Enter your CIS income to see the refund you could be owed.
How CIS tax refunds work
If you work as a subcontractor in construction, the contractors who pay you must deduct tax under the Construction Industry Scheme (CIS) — 20% if you are registered, 30% if you are not — and pay it to HMRC on your behalf. It is treated as an advance payment towards your Income Tax and National Insurance.
The catch: that deduction is taken from your gross labour income, before any of your tax-free personal allowance or business expenses are taken into account. So the amount deducted is almost always more than you actually owe — and the difference comes back to you as a refund when you file your Self Assessment.
Who is due a refund?
Frequently Asked Questions
Why do CIS subcontractors get a tax refund?
Under the Construction Industry Scheme, contractors deduct 20% (or 30% if you are not registered) from your labour payments and send it to HMRC as an advance payment towards your tax and National Insurance. When you file your Self Assessment, your actual liability is usually lower — because of your personal allowance and business expenses — so HMRC refunds the difference. Many subcontractors are owed a substantial sum each year.
How accurate is this calculator?
It gives a realistic estimate for a typical labour-only subcontractor with no other income. It applies the current personal allowance, income tax bands, and Class 4 National Insurance. It does not account for other income, payments on account, student loan repayments, the High Income Child Benefit Charge, or CIS deducted on materials. Treat the result as a guide — we calculate the exact figure when we prepare your return.
How do I actually claim my CIS refund?
You claim it through your Self Assessment tax return. You report your income, the CIS tax already deducted (from your monthly deduction statements), and your allowable expenses. HMRC then repays any overpayment, usually within a few weeks of filing. We handle the whole process for subcontractors across London — gathering your figures, maximising allowable expenses, and filing the claim.
What expenses can I claim as a subcontractor?
Common allowable expenses include tools and equipment, protective clothing, travel to temporary sites, vehicle running costs, public liability insurance, phone and admin costs, and accountancy fees. Claiming everything you are entitled to increases your refund — which is exactly where an accountant who knows CIS pays for itself.
Related: CIS Tax Services, Contractor Accountants, the Contractor Take-Home Calculator, and Self Assessment.
Let us claim it back for you.
We handle CIS refund claims for subcontractors across London — maximising your expenses and filing it right.
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