How to Claim Back CIS Deductions Through Self Assessment
Step-by-step guide to reclaiming overpaid CIS tax through Self Assessment. How to get your CIS refund from HMRC, avoid common mistakes, and key deadlines.
Key Actions
- Collect all CIS payment statements from your contractors
- File your Self Assessment return including CIS deduction amounts
- Check your tax calculation to see if you're owed a refund
- Contact HMRC if a contractor can't provide replacement statements
- Set up a system to store CIS statements digitally each month
If you work as a CIS subcontractor, your contractors deduct tax from your payments throughout the year and send it to HMRC. But those deductions are advance payments — not your final tax bill. When you file your Self Assessment, you may find you've overpaid. Here's how to get that money back.
How CIS Deductions Work as Tax Credits
Every time a contractor pays you, they withhold either 20% (registered) or 30% (unregistered) of the labour portion and send it to HMRC on your behalf.
At the end of the tax year, HMRC adds up all those deductions and compares them to your actual tax and National Insurance bill. If the deductions exceed what you owe, the difference comes back to you as a refund.
Example:
| Item | Amount |
|---|---|
| Total CIS income (2025/26) | £48,000 |
| Allowable expenses | £6,000 |
| Taxable profit | £42,000 |
| Income Tax due | £5,886 |
| Class 4 National Insurance due | £1,766 |
| Total tax liability | £7,652 |
| CIS deducted at 20% | £9,600 |
| Refund due | £1,948 |
In this case, the subcontractor overpaid by £1,948 because CIS was calculated on gross income, while the actual tax bill accounts for expenses and allowances.
Claiming Back CIS as a Sole Trader or Partner
If you're a sole trader or in a partnership, you reclaim CIS through your Self Assessment tax return.
Step 1: Gather your CIS payment statements
Contractors provide a statement each time they pay you. Each statement shows the gross amount, materials deducted, CIS deduction, and net payment. You need all of these for the tax year.
Step 2: File your Self Assessment return
When completing your return:
- Record the full invoice amounts as your income (the gross figures, not what you received)
- Enter your allowable business expenses
- In the CIS deductions section, enter the total amount deducted by all contractors during the year
Step 3: HMRC calculates your position
HMRC works out your tax and National Insurance, then subtracts the CIS already paid. Three outcomes are possible:
- Refund due — You overpaid. HMRC sends the difference back to you
- Nothing to pay — Deductions matched your liability exactly
- Balance to pay — Your tax bill exceeds what was deducted (less common at 20%)
Step 4: Receive your refund
If you're owed money, HMRC typically processes refunds within 4-6 weeks of receiving your return. The refund goes to the bank account linked to your Self Assessment.
What About Limited Companies?
If you operate through a limited company, the process is different — you don't use Self Assessment. Instead, CIS deductions offset against your PAYE liability through Employer Payment Summaries (EPS). The rest of this guide focuses on sole traders and partnerships.
What If You've Lost CIS Statements?
Without statements, you can't prove how much was deducted. Here's what to do:
Ask the contractor first. They're required to keep records and can issue replacement statements.
If the contractor has stopped trading, contact HMRC PT Operations with:
- Your name, address, and UTR
- The contractor's name and address
- Their tax reference (if you have it)
- Approximate payment dates
- Why you can't get the statement
HMRC can check their records and confirm the deductions made.
Common Reasons People Miss Out on CIS Refunds
Not filing Self Assessment
This is the biggest one. If you don't file a return, you can't reclaim overpaid CIS. There's no other route to get that money back.
Filing late
You can still claim, but you'll face late filing penalties (£100 initially, rising over time). The refund may be reduced by the penalty amount.
Forgetting to include CIS deductions
Some people file their return but don't enter the CIS figures. Double-check the CIS section before submitting.
Not claiming allowable expenses
The more legitimate expenses you claim, the lower your tax bill — and the larger your potential refund. Common CIS expenses include tools, travel to sites, protective clothing, and vehicle costs.
Key Deadlines
| Deadline | What it means |
|---|---|
| 5 April 2026 | End of the 2025/26 tax year — gather all statements |
| 31 October 2026 | Paper Self Assessment deadline (for 2025/26) |
| 31 January 2027 | Online Self Assessment deadline (for 2025/26) |
| 31 January 2027 | Payment deadline for any tax owed (for 2025/26) |
Filing earlier means getting your refund sooner. You don't have to wait until January.
How Much Could You Get Back?
The refund amount depends on your income, expenses, and personal allowances. Here are rough examples for the 2025/26 tax year:
| Annual CIS income | Expenses claimed | CIS deducted (20%) | Approximate refund |
|---|---|---|---|
| £30,000 | £4,000 | £6,000 | £2,500-£3,500 |
| £45,000 | £5,000 | £9,000 | £1,000-£2,000 |
| £60,000 | £8,000 | £12,000 | £500-£1,500 |
These are estimates. Your actual position depends on your full tax calculation, including any other income and personal circumstances.
Frequently Asked Questions
How long does it take to receive a CIS refund from HMRC?
HMRC typically processes Self Assessment refunds within 4-6 weeks of receiving your return. Filing early in the tax year (April-June) often means faster processing.
Can I claim back CIS without filing a Self Assessment return?
No. Self Assessment is the only route for sole traders and partners to reclaim overpaid CIS. If you don't file, the money stays with HMRC.
What if my CIS deductions don't match what HMRC has on record?
Use your own payment statements as evidence. If a contractor reported incorrect figures, ask them to submit a correction. HMRC will reconcile the amounts during processing.
Can I claim CIS refunds for previous years?
Yes. You can claim overpayment relief for up to 4 years after the end of the tax year the deductions relate to. If you've missed claiming CIS deductions from earlier years, it's worth filing those returns to recover the money.
This guide is for informational purposes only and does not constitute tax, legal, or financial advice. Tax rules change frequently. Always verify current requirements on GOV.UK or consult a qualified accountant for your specific situation.
Official Sources
- Pay tax and claim back deductions - GOV.UK
- Self Assessment tax returns - GOV.UK
- Construction Industry Scheme (CIS) - GOV.UK