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Tax calculator

CIS Tax Refund Calculator

Estimate the tax refund you are owed as a CIS subcontractor. Enter your gross CIS income, your 20% or 30% deduction and your expenses for the 2026-27 tax year to see the CIS taken at source, your real income tax and Class 4 NI bill, and the refund in between.

Free, no signup2026/27 ratesVerify at gov.uk
Your CIS year
Total payments before CIS was deducted (the labour amount CIS is charged on, excluding materials and VAT).
£
20% if you are registered with HMRC, 30% if not.
Allowable costs: tools, work travel, protective clothing, insurance. Leave at 0 if unsure.
£
Other self-employed or untaxed income in the year. Leave at 0 if all your income is CIS.
£
Estimated CIS refund
£2,168
HMRC took £8,000 in CIS, but your real bill is only £5,832. You are likely owed the difference back.
CIS deducted at source (20%)On £40,000 gross CIS income£8,000.00
Taxable profitAfter £12,570 personal allowance£22,430
Income tax due£4,486.00
Class 4 National Insurance£1,345.80
Actual Self Assessment bill£5,831.80
Estimated refund£2,168.20
Why a refund is common: CIS is deducted from your gross pay with no personal allowance and no expenses taken off, so most subcontractors have paid more than their real bill. Your first £12,570 of profit is tax-free, and expenses cut it further. Employed as well, or want your salary side? Use the take-home pay calculator.
2026/27 rates: CIS 20%, income tax 20% / 40% / 45%, Class 4 NI 6% / 2%. Class 2 NI is £0 above the £7,105 Small Profits Threshold. England, Wales and NI (Scotland sets its own income tax bands). General information, not tax advice.
Simon Chadwick
Simon Chadwick
Founder, Orbit Money
Method: gov.uk CIS deduction rates, income tax bands and Class 4 NIUpdated: 17 July 2026Sources: gov.uk/what-you-must-do-as-a-cis-subcontractor

How a CIS tax refund works

The Construction Industry Scheme (CIS) is how HMRC collects tax from construction subcontractors before they file. When a contractor pays you, they deduct 20% if you are registered, or 30% if you are not, from the labour part of the payment and send it to HMRC. Materials and VAT are left out of that deduction. Those deductions are advance payments towards your tax and National Insurance, not a final tax. At the end of the year your real bill is income tax and Class 4 NI on your profit, which is your income minus allowable expenses. Because the deduction ignores your personal allowance and your costs, the CIS taken is usually more than you owe, and the gap comes back to you as a refund.

Working out your real Self Assessment bill

Your real bill starts from profit. Your first £12,570 of profit is covered by the personal allowance, so it is tax-free. Above that, income tax is 20% up to £50,270, 40% up to £125,140 and 45% beyond. On top of income tax you pay Class 4 National Insurance: 6% on profit between £12,570 and £50,270, then 2% above £50,270 for 2026-27. Class 2 National Insurance is £0 to pay once your profit clears the £7,105 Small Profits Threshold, because you are treated as having paid it. This calculator adds income tax and Class 4 together to get your real bill, then subtracts the CIS already deducted to show your refund.

A worked example

Say you took £40,000 of gross CIS income in 2026-27, all at the 20% rate, with £5,000 of allowable expenses. The contractor deducted £8,000 in CIS along the way. Your profit is £40,000 minus £5,000, so £35,000. After the £12,570 personal allowance, £22,430 is taxable, giving income tax of £4,486. Class 4 NI at 6% on the same £22,430 adds £1,345.80, so your real bill is about £5,832. Subtract that from the £8,000 already taken and your estimated refund is around £2,168.

Expenses are what grow your refund

Every allowable expense lowers your profit, which lowers your real bill and lifts your refund. Common ones for subcontractors are tools and equipment, protective clothing and boots, travel to temporary sites, insurance, phone and admin costs, and accountant fees. Materials you paid for count too. The flip side is simple: if you record no expenses, you leave refund on the table. Keeping receipts through the year is the single biggest thing that changes how much comes back, so treat this tool as a way to size the refund, then log your costs properly before you file.

Registered at 20% or unregistered at 30%

If you are registered with HMRC under CIS, contractors deduct 20%. If you are not registered, or a contractor cannot verify you, they must deduct 30% instead. Registering is free and straightforward, and it drops the rate by a third, so most subcontractors are better off registered. Either way the deduction is still only an advance payment, so an unregistered worker on 30% has more sitting with HMRC to reclaim through Self Assessment. Switch the rate in the calculator to see the difference on your own figures.

Frequently asked questions

How is a CIS tax refund calculated?
Your contractor deducts 20% (or 30% if you are not registered) from your labour payments and sends it to HMRC as an advance payment towards your tax. At the end of the year your real bill is income tax and Class 4 National Insurance on your profit, which is your income minus allowable expenses. Your refund is the CIS already deducted minus that real bill. For example, on £40,000 of gross CIS income with £5,000 of expenses, £8,000 is deducted at 20% but the real bill is about £5,832, so the refund is roughly £2,168.
Why do CIS subcontractors usually get a refund?
Because CIS is taken from your gross pay with no personal allowance and no expenses removed first. Your first £12,570 of profit is tax-free for 2026-27, and tools, work travel, insurance and other allowable costs cut your taxable profit further. So the flat 20% or 30% taken at source is almost always more than the tax and National Insurance you owe, which is why most subcontractors are owed money back.
What is the CIS deduction rate, 20% or 30%?
It is 20% if you are registered with HMRC under the Construction Industry Scheme, and 30% if you are not registered or the contractor cannot verify you. Both are deducted from the labour part of your payments only, not from materials or VAT. Registering is free and drops the rate from 30% to 20%, so it is worth doing if you have not already.
How do I claim my CIS tax refund?
You claim it through Self Assessment. You file a tax return after the 5 April year end reporting your income, expenses and the CIS deductions already taken. HMRC works out your real bill, credits the CIS you have paid, and refunds any overpayment. The deadline for an online return is 31 January, and refunds are usually paid within a few weeks of filing.
Is CIS deducted from materials and VAT?
No. The CIS deduction applies to the labour element only. The cost of materials, plant hire, and any VAT you charge are excluded before the 20% or 30% is worked out. That is why this calculator asks for your gross CIS income, meaning the labour payments CIS was charged on, rather than your total invoices including materials.
Do I still pay National Insurance under CIS?
Yes. As a CIS subcontractor you are a sole trader, so you pay Class 4 National Insurance on your profit: 6% between £12,570 and £50,270, then 2% above that for 2026-27. Class 2 National Insurance is £0 to pay once your profit clears the £7,105 Small Profits Threshold, because you are treated as having paid it. This calculator includes Class 4 in your real bill before working out the refund.
What expenses can I claim on a CIS tax return?
Allowable costs that reduce your taxable profit include tools and equipment, protective clothing, travel to temporary sites, public transport or mileage, insurance, phone and admin costs, and accountant fees. Materials are also deductible where you paid for them. The more genuine expenses you record, the lower your real tax bill and the larger your CIS refund, so keep receipts through the year.

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Simon Chadwick
About the author
Simon Chadwick
Founder of Orbit Money

Simon is the founder of Orbit Money, a tool that helps people track subscriptions and recurring spend. He builds Orbit's free money calculators and writes about personal finance for UK and Australian readers.

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This tool is a guide, not tax or financial advice.