How does Self Assessment work for a CIS subcontractor?
CIS deductions made by contractors are advance payments towards your tax position. At the end of the tax year, a sole-trader subcontractor reports their business results through Self Assessment.
Your return brings together the full business income, allowable expenses and CIS deductions already suffered. HMRC then calculates the tax and National Insurance position.
What CIS income goes on the tax return?
HMRC tells sole traders and partners to record the full amounts shown on their invoices as business income.
Invoice £2,000 — CIS deducted £400
The subcontractor does not simply record the £1,600 net payment as turnover. The business income and CIS deduction are dealt with separately.
Where are CIS deductions reported?
CIS deductions are recorded in the dedicated CIS deductions part of the self-employment reporting process.
HMRC's current full self-employment form includes a specific field for total Construction Industry Scheme deductions taken from subcontractor payments.
Can you deduct CIS business expenses?
Yes, where the normal self-employed expense rules are met.
Typical construction-related categories can include qualifying:
- Tools and equipment.
- Mileage and business travel.
- Protective clothing and PPE.
- Materials.
- Insurance and professional costs.
- Phone and other business expenses.
See our CIS Allowable Expenses Guide.
Why do deduction statements matter?
Payment and Deduction Statements help support the CIS credit you report. Reconcile the total deductions against contractor statements before filing.
What are the current Self Assessment deadlines?
For the 2025/26 tax year currently being filed, HMRC's published dates are:
| Date | Current 2025/26 requirement |
|---|---|
| 5 October 2026 | Tell HMRC you need a return where the registration requirement applies. |
| 31 October 2026 | Standard paper-return deadline. |
| 31 January 2027 | Online return and normal tax-payment deadline. |
The 2025/26 tax year ended on 5 April 2026, but the standard online filing deadline falls in January 2027.
How does a CIS refund arise?
HMRC calculates the tax and relevant National Insurance due and gives credit for contractor deductions.
Where the verified CIS deductions and other relevant tax payments exceed the amount ultimately due, an excess may be repayable.
A subcontractor can instead have no repayment or still owe additional tax, depending on the final calculation.
What if the CIS deductions are not enough?
If the final liability exceeds the deductions and other tax credits, the balance remains payable under the Self Assessment rules.
Do limited companies use an individual's Self Assessment return?
No.
HMRC has a separate CIS set-off procedure for company subcontractors, generally involving the company's PAYE scheme and Employer Payment Summary.
Which records should you prepare before filing?
- Sales invoices.
- Payment and Deduction Statements.
- Bank records.
- Expense receipts.
- Mileage and travel records.
- Tool and equipment invoices.
- Any other taxable income information.
Reviewed & Updated
18 August 2026
2025/26
GO TAX REFUNDS
HMRC / GOV.UK
CIS Self Assessment FAQs
Do CIS subcontractors file Self Assessment?
Individual self-employed subcontractors normally report their trading income and CIS deductions through Self Assessment.
Do I declare the amount after CIS was deducted?
HMRC says to report the full invoice amounts as income and report the contractor deductions separately.
Does CIS already pay all my tax?
Not necessarily. CIS deductions are advance payments and the final position is calculated through the tax return.
When is my 2025/26 online return due?
HMRC's standard online deadline for the 2025/26 return is 31 January 2027.
Official HMRC Sources
GOV.UK — Pay tax and claim CIS deductions GOV.UK — Self Assessment deadlines HMRC — Self-employment supplementary pagesNeed help with your CIS Self Assessment?
Go Tax Refunds can help review your contractor deductions, income and allowable business expenses.
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