Self-Employed & CIS

CIS Tax Refund Calculator

Last updated: 09 September 2026 · 2026/27 UK tax year

Because 20% is deducted from all your earnings, most CIS subcontractors overpay tax. Factor in your expenses to see how much HMRC might owe you.

The Construction Industry Scheme (CIS) is a tax collection mechanism used by HMRC for construction subcontractors in the UK. Under CIS, contractors deduct money from a subcontractor's payments at source — typically 20% for registered subcontractors or 30% for unregistered ones — and pass it to HMRC as an advance payment against the subcontractor's tax liability. This is not a final tax bill; it is a deduction on account.

Because CIS deductions are often made at a flat 20% regardless of your actual tax rate, and because you may have legitimate business expenses that reduce your taxable profit, the vast majority of CIS subcontractors are owed a tax refund at the end of the year. The average CIS refund is estimated to be between £1,000 and £3,000 per tax year. To claim your refund, you must submit a Self Assessment tax return — HMRC does not automatically issue refunds. Use this calculator to estimate how much you may be owed.

Your Income

Gross CIS Payments Received

CIS Tax Deducted (usually 20%)

Business Expenses

Materials

Tools / Equip

Travel / Van

Other

Expenses reduce your taxable profit, which increases your likely refund.

CIS Tax Verdict

Estimated Refund: £2,170.00

Because your contractor already deducted £8,000.00 and your actual tax bill (including NI) is only £5,830.00, HMRC owes you money.

Taxable Profit (after expenses)£35,000.00

Income Tax Owed£4,484.20

Class 4 NI Owed£1,345.80

Total Tax Liability£5,830.00

CIS Already Deducted- £8,000.00

How to claim your CIS refund →

Disclaimer: This calculator provides an estimate based on standard HMRC tax rules for the 2026/27 tax year. It does not account for cumulative PAYE codes, previous underpayments, or specific employer payroll configurations. It is not professional financial advice. For definitive figures, always refer to your official payslip or your HMRC Personal Tax Account.

How CIS tax refunds work

If you're a subcontractor in the Construction Industry Scheme (CIS), your contractor deducts money from your payments and passes it to HMRC. For registered workers, this deduction is 20%. For unregistered workers, it's 30%.

These deductions act as advance payments towards your tax and National Insurance bill. However, a flat 20% deduction almost always means you've overpaid tax, because it doesn't take into account:

Your Personal Allowance: You can earn £12,570 a year completely tax-free.
Your Business Expenses: Tools, travel, and materials reduce your taxable profit.

Allowable expenses for CIS workers

To maximize your refund legitimately, you should claim all allowable business expenses. The most common ones include:

Materials and supplies: Anything you buy to complete the job.
Tools and equipment: Drills, saws, hand tools, and their maintenance.
Travel and vehicle costs: Fuel, van insurance, repairs, or claiming the flat rate mileage (45p per mile for the first 10,000 miles).
Clothing: Protective workwear and uniforms (but not everyday clothing).
Admin: Phone bills, internet, and accountant fees.

How to claim your money back

To get your CIS tax refund, you must complete a Self Assessment tax return after the tax year ends (5 April). You'll declare your total income, your expenses, and the total amount of CIS tax already deducted.

HMRC will calculate your actual tax bill, subtract the CIS deductions you've already paid, and refund the difference directly to your bank account.

Related Guides

CIS Payslip Explained

Understand the 20% deductions on your payslip and what Gross Payment Status means.

Self-Employed Tax

General tax calculator for self-employed individuals and sole traders.

How to claim your refund

Step by step guide to getting your money back from HMRC.

Frequently asked questions

Why do I get a tax refund under CIS?

Under the Construction Industry Scheme (CIS), contractors deduct 20% or 30% from your payments. This doesn't account for your tax-free personal allowance or your business expenses, so most CIS workers end up overpaying tax and receive a refund when they file their Self Assessment.

What expenses can I claim as a CIS worker?

You can claim for tools, equipment, materials, van running costs, travel between sites, protective clothing, and phone bills (business use portion).

When can I claim my CIS tax refund?

You can claim your refund after the tax year ends on 5 April, by submitting your Self Assessment tax return. Many workers submit their returns in April or May to get their refund quickly.