CIS Tax Refund Calculator: How Much Can Construction Workers Claim Back?
Construction workers on the Construction Industry Scheme (CIS) often overpay tax by thousands of pounds each year. Contractors deduct 20% (or 30% if not registered) from your payments and pass it to HMRC. But this deduction is calculated on your gross pay — not your profit after expenses. Most CIS subcontractors are due a significant tax refund.
Why CIS subcontractors get refunds
The 20% CIS deduction is an advance payment towards your tax bill — it is not your final tax liability. Your actual tax is calculated on your profit (income minus expenses), and most construction workers have substantial expenses. Materials, tools, vehicle costs, protective clothing, training, and insurance can easily total thousands of pounds per year.
For example, a plumber on CIS earning £40,000 gross would have £8,000 deducted by contractors. But after £8,500 of business expenses, their taxable profit is only £31,500. Their actual Income Tax plus NICs totals approximately £5,500 — meaning they are due a refund of £2,500.
Common CIS expenses to claim
- Materials and supplies: Copper pipe, fittings, cable, timber, fixings — keep all receipts
- Tools and equipment: Power tools, hand tools, ladders, safety equipment
- Vehicle costs: Mileage at 45p/25p per mile, or actual fuel, insurance, servicing apportioned for business
- Protective clothing: Hard hats, safety boots, hi-vis, goggles, gloves
- Training and certification: CSCS cards, NVQs, gas safe, first aid
- Insurance: Public liability, tool insurance, vehicle business use
- Accommodation: Hotel costs when working away from home
- Phone and internet: Business proportion of bills
- Accountancy fees: Cost of preparing your tax return
Track your expenses throughout the year with our free CIS Expense Tracker spreadsheet. Read our complete CIS tax refund guide for step-by-step instructions on claiming your money back from HMRC.
How CIS Tax Refunds Work
Under the Construction Industry Scheme (CIS), contractors deduct tax from payments to subcontractors and pass it directly to HMRC. These deductions act as advance payments toward your final tax bill.
- Registered subcontractors — 20% deducted from gross payments
- Unregistered subcontractors — 30% deducted from gross payments
- At tax year end, you file a Self Assessment tax return
- HMRC calculates your actual tax liability based on profit (income minus expenses)
- If CIS deductions exceed your tax liability, you receive a refund
- If your tax liability exceeds CIS deductions, you owe additional tax
Most CIS subcontractors receive a refund because the flat 20% or 30% deduction rate is often higher than the actual effective tax rate after expenses and the Personal Allowance are applied.
Frequently Asked Questions
How much CIS tax can I claim back?
The amount depends on your total taxable income, allowable expenses, and how much CIS tax was deducted. If your actual tax liability (Income Tax + Class 2/4 NICs) is less than the CIS deductions already taken, HMRC will refund the difference. Most CIS subcontractors who claim all allowable expenses receive a significant refund. Use our calculator above to get your personal estimate.
What is the difference between 20% and 30% CIS deductions?
Registered CIS subcontractors have tax deducted at
20% of gross payments. Unregistered subcontractors have tax deducted at
30%. Registering with HMRC as a CIS subcontractor immediately reduces your deduction rate from 30% to 20%, meaning you keep significantly more of your money throughout the year.
Register for CIS on Gov.uk.
What expenses can I claim as a CIS subcontractor?
Common allowable expenses include: tools and equipment, protective clothing (PPE), vehicle costs (mileage at 45p/mile for first 10,000 miles, then 25p), fuel for work travel, accommodation when working away from home, phone costs used for work, trade subscriptions, public liability insurance, accountancy fees, and training courses directly related to your work. Keep all receipts and records. You cannot claim for travel between home and your regular workplace.
When will I get my CIS tax refund?
After submitting your Self Assessment tax return online, HMRC typically processes CIS refunds within
4-8 weeks. Submitting online is faster than paper returns. Ensure your bank details are up to date with HMRC to receive your refund by direct bank transfer. You can check your refund status through your
HMRC Personal Tax Account.
Do I need to register for Self Assessment as a CIS subcontractor?
Yes. All CIS subcontractors must register for Self Assessment, even if you're also employed elsewhere. You need to file a tax return by 31 January following the end of the tax year (which runs 6 April to 5 April). This is how you claim your CIS refund. If you don't register and file, you won't receive any refund you're entitled to, and HMRC may issue penalties.
How do I register for CIS?
You can register as a CIS subcontractor online through
HMRC's CIS registration page. You'll need your UTR (Unique Taxpayer Reference), National Insurance number, and business details. Once registered, contractors will deduct 20% instead of 30% from your payments. Registration is free and can be done at any time.
Sources & Methodology
All calculations are verified against official HMRC thresholds and rates for the 2026/27 tax year. Class 2 NIC is £3.45/week (£179.40/year) for profits above £6,725. Class 4 NIC is 6% on profits between £12,570 and £50,270, and 2% above. Calculations are for guidance only — consult a qualified accountant for personalised advice.
What You Should Do Next
- Register for CIS — If you're on 30% deductions, register immediately to drop to 20%. Register on Gov.uk.
- Keep detailed expense records — Every receipt increases your refund. Use a dedicated business bank account and apps like Receipt Bank or Expensify.
- File your Self Assessment early — Don't wait until January. Filing early means getting your refund sooner. Use HMRC's free online service or an accountant.
- Consider the VAT Flat Rate Scheme — If your turnover exceeds £85,000, the CIS flat rate VAT scheme can simplify your VAT returns. Try our VAT Calculator.