How to claim a CIS refund yourself

How CIS refunds happen

When you work for a contractor in construction, they take a percentage off the labour part of each payment and send it to HMRC: 20% if you're registered for CIS, 30% if you're not. That money is credited to you as tax already paid.

The catch is that CIS is worked out on your labour before two big things:

1. Your costs. Tools, van, fuel, protective clothing, insurance and phone all reduce your taxable profit, but the contractor doesn't know about them.
2. Your Personal Allowance. The first £12,570 of profit is normally tax-free, but CIS is taken from your very first pound.

So once your Self Assessment return works out your real bill on your actual profit, many subbies find they've paid more than they owe. The difference comes back to you as a refund.

Worked example: a 2025/26 refund

Dan is a self-employed carpenter, registered for CIS, working through 2025/26 (6 April 2025 to 5 April 2026). He lives in England.

Now the tax on that profit, using 2025/26 rates:

• Income Tax: £25,000 − £12,570 Personal Allowance = £12,430 taxable × 20% = £2,486.00
• Class 4 NI: (£25,000 − £12,570) × 6% = £745.80
• Total bill: £3,231.80

Dan has already paid £6,000 through CIS, so his estimated refund is £6,000 − £3,231.80 = £2,768.20.

If Dan had claimed no costs at all, his profit would be £30,000 and his bill £4,531.80, so his refund would drop to £1,468.20. Claiming every allowable cost matters.

What you need before you start

• Your UTR (Unique Taxpayer Reference). You'll have one if you registered as self-employed. It's on letters from HMRC and in your online account.
• Your HMRC online account login (Government Gateway or GOV.UK One Login).
• Every CIS payment and deduction statement for the tax year, from every contractor. Add up the gross pay, materials and CIS deducted.
• Records of your costs: receipts, bank statements and a mileage log if you claim mileage.
• Your bank details, so HMRC can pay the refund straight into your account.

If you haven't registered for Self Assessment yet, do that first. Our guide to registering as self-employed under CIS explains how.

How to claim, step by step

1. Add up your CIS statements

Contractors must give you a statement for each tax month they pay you (tax months run from the 6th to the 5th). Each one shows the gross amount, any materials, and the CIS deducted. Total them for the year. If one is missing, ask for it — and check your online account, which shows what contractors reported.

2. Check CIS was only taken on labour

CIS should never be deducted from materials, VAT, plant hire or consumables you paid for. If a contractor took 20% off the whole invoice, you've overpaid. That still comes back through your return, but it's worth raising with the contractor so it doesn't keep happening. Our guide to CIS deductions explains what should and shouldn't be included.

3. Fill in the self-employment section

Sign in and start your Self Assessment return for the year. In the self-employment section you enter:

• your total turnover — the gross amount you were paid, including materials, before CIS was taken off;
• your allowable expenses, by category (or as a single total if your turnover is under the limit HMRC sets for that);
• the total CIS deductions made by contractors, in the box for deductions on account of tax.

Getting turnover right is the most common mistake: use the gross figure, not what landed in your bank.

4. Check the calculation and submit

The online return works out your tax and Class 4 NI and shows the result. If the CIS you've entered is more than your bill, you'll see an amount HMRC owes you. Check it against your own estimate, add your bank details when asked, and submit.

5. Wait for the repayment

HMRC processes the return and pays the refund. (HMRC also has an online form that sole traders can use to claim back deductions during the tax year in some cases — GOV.UK explains when.) Most online claims are paid within weeks, though checks can take longer — for example if the CIS figures you entered don't match what contractors reported. HMRC may also hold back money if you have another tax payment due soon.

Deadlines

You don't have to wait until January. Filing early doesn't make the refund smaller, and it gets the money back to you sooner. See Self Assessment deadlines and penalties for the paper deadline and what happens if you're late.

Claiming for earlier years

If you've worked under CIS before and never claimed, the money isn't necessarily lost:

• You never filed a return for that year: you can still send one. HMRC generally lets you claim overpaid tax for up to four years after the end of the tax year.
• You filed but missed costs: you can amend the return online within 12 months of the 31 January deadline for that year. After that, you can make an overpayment relief claim in writing, still within four years.

So in the 2026/27 tax year, the earliest year you can normally still claim for is 2022/23, and the time limit for that runs out on 5 April 2027.

If you're a limited company

Everything above is for sole traders. If you trade through a limited company, CIS deducted from the company is set against the company's own PAYE and National Insurance bill through its payroll submissions. Any amount left over can be reclaimed from HMRC, but not through Self Assessment. Speak to whoever runs your company payroll.

Do it yourself or pay a firm?

Plenty of firms will claim for you, usually for a fixed fee of a few hundred pounds or a percentage of the refund. They can save you time, but they use the same return you can file yourself. Our comparison of CIS refund companies sets out what they charge, so you can decide whether it's worth it.