If you're a self-employed subcontractor, you claim CIS back by filing your Self Assessment tax return after the tax year ends on 5 April. Enter your pay before deductions as income, your expenses, and the total CIS your contractors took off. HMRC works out what you owe and pays back anything taken over that. Filing online, as early as you can, gets the money back fastest.
Why most subbies are owed money back
CIS isn't an extra tax. It's an advance payment towards your own Income Tax and National Insurance, taken off by the contractor before you're paid. The problem is that it's a flat 20% (or 30% if you're not registered) taken from the first pound of labour.
When your real tax bill is worked out at the end of the year, three things bring it down that CIS ignores:
- Your personal allowance: the first £12,570 of profit is tax-free.
- Your expenses: tools, PPE, materials you paid for, phone, insurance and accountant fees all come off your profit.
- Your mileage: driving to temporary sites at HMRC's rate of 55p a mile for the first 10,000 miles (from April 2026).
So for most subbies, the CIS taken during the year is more than the tax actually owed, and the difference comes back as a refund. Someone on £45,000 of labour at 20%, with £3,000 of expenses and 8,000 business miles, is owed roughly £2,500.
What you need before you start
- Your UTR (Unique Taxpayer Reference) and a Government Gateway login for HMRC online. Your UTR is shown in the HMRC app and your HMRC online account. If you're on 20% CIS as a sole trader, you'll already have a UTR, because you need one to register for CIS.
- Every monthly payment and deduction statement from every contractor you worked for that year. These show what you were paid and how much CIS was taken.
- Your total pay before deductions, including materials your contractors paid you for.
- Your expenses, ideally with receipts. Not sure what counts? See what expenses CIS subcontractors can claim.
- Your business miles for the year, if you drive to temporary sites.
- Your bank details, so HMRC can pay the refund straight into your account.
The six steps
1. Make sure you're registered for Self Assessment
You need a UTR and an HMRC online account to file. If you've never filed a tax return before, register for Self Assessment first. It can take a couple of weeks for your activation code to arrive by post, so don't leave it until January.
2. Collect your payment and deduction statements
Contractors must give you a statement for each tax month in which they paid you and took CIS off (a tax month runs from the 6th to the 5th). Add up the CIS deducted across all of them. That total is the figure you'll put on your return.
If a statement is missing, ask the contractor for it. Giving you one is a legal requirement, not a favour. Keep your own records too, because HMRC checks the figure you claim against what your contractors reported.
3. Work out your income and expenses
Your income is everything contractors paid you before CIS was taken off, including materials they reimbursed. Then add up your allowable expenses and your mileage allowance. Income minus expenses and mileage is your taxable profit.
4. File your return online after 5 April
You can file for a tax year from the day after it ends (6 April). In the self-employment section, enter:
- your turnover: pay before CIS deductions
- your allowable expenses, including mileage
- the total CIS deductions taken by contractors, in the box for deductions on payment and deduction statements
5. Let HMRC work out the refund
HMRC calculates your Income Tax and Class 4 National Insurance, takes off the CIS you've already paid, and shows you the result before you submit. If it's a refund, make sure your bank details are on the return.
6. Track the repayment
You can check the progress of your refund in your HMRC online account. Many come through within a few weeks, but HMRC's security checks, or a mismatch with your contractors' figures, can make it take longer.
Deadlines for 2025/26 and 2026/27
| Tax year | File from | Paper by | Online by |
|---|---|---|---|
| 2025/26 | 6 Apr 2026 | 31 Oct 2026 | 31 Jan 2027 |
| 2026/27 | 6 Apr 2027 | 31 Oct 2027 | 31 Jan 2028 |
If you owe tax rather than getting a refund, the payment is due by the same 31 January online deadline. If you've missed returns for earlier years, you can usually still claim, but late filing penalties can apply, so it's worth speaking to HMRC or an accountant first.
If you've joined Making Tax Digital for Income Tax (for self-employed income over £50,000 from April 2026), you'll send quarterly updates through MTD software, but your CIS is still settled when you finish the year with your tax return.
What slows a refund down
- The CIS figure doesn't match. If the total you claim is different from what your contractors reported to HMRC, the refund can be held while HMRC checks it. Use the figures from your statements, not a guess.
- Entering pay after deductions as income. A common mistake. Your income should be the figure before CIS. Putting in what landed in the bank and then claiming the CIS on top makes the numbers not add up.
- Missing statements. Chase them as you go, not in January.
- Filing on paper. Paper returns take longer to process than online ones.
- Wrong or missing bank details. HMRC may send a cheque instead, or hold the payment.
Should you pay a refund company?
You don't have to. Filing your own Self Assessment return is free, and HMRC works out the refund for you. Refund companies and accountants charge a fixed fee or a percentage of the refund to do it for you.
That can be worth it if your year was complicated: several income sources, a big gap in your records, or years you've missed. But if you've kept your statements and expenses, you can often do it yourself. Either way, knowing your rough figure first means you can tell whether a quote is fair.
If you're a limited company
This guide is for sole traders and partners. Limited companies don't claim CIS back on a Self Assessment return. Instead, the company sets the CIS deductions against its PAYE bill through its payroll (on the Employer Payment Summary), and claims any leftover amount back from HMRC after the tax year ends.
Keeping it easy next year
The hardest part of claiming CIS back is usually finding the numbers. DayGraft keeps them as you go: every day's labour and materials, the CIS worked out on each one, your expenses with receipt photos, and your mileage from site postcodes. At the end of the year you can export it all as a CSV for yourself or your accountant. With DayGraft Pro, the app also shows a running estimate of your refund all year.
Sources (last checked 23 October 2026): Pay tax and claim back CIS deductions — GOV.UK · CIS guide for contractors and subcontractors (CIS340) — GOV.UK · Self Assessment deadlines — GOV.UK · Register for Self Assessment — GOV.UK · CIS subcontractors: submit your tax return early — LITRG
This guide is general information, not tax advice. If your situation is complicated, speak to an accountant or HMRC.