If you're a CIS subcontractor working as a sole trader, the money your contractors took off your pay isn't lost. GOV.UK says the deductions "count as advance payments towards your tax and National Insurance bill". Your Self Assessment return is where they're taken off your tax bill, and GOV.UK says that if you're due a refund, HMRC pays the money back. Both depend on adding them up properly first.
This guide shows how to get the two totals the return asks for from a year of monthly statements.
The short answer
GOV.UK tells sole traders and partners to do two things on their Self Assessment return:
- record your total pay before deductions as income
- record the total deductions in the "CIS deductions" field
HMRC then works out your tax and National Insurance and takes off what was already deducted. If your contractors deducted more than your bill, the difference comes back to you. Any tax still owed is due by 31 January after the end of the tax year.
So the job is adding up two columns, correctly, for the right tax year.
Step 1: Get every statement for the tax year
Each contractor should give you a payment and deduction statement within 14 days of the end of each tax month. A tax month runs from the 6th of one month to the 5th of the next, so a tax year has 12 statement periods from each contractor you worked for:
- the first ends 5 May
- the last ends 5 April
For the 2025–26 tax year (the return due by 31 January 2027) that means statements for tax months ending 5 May 2025 through to 5 April 2026.
If one is missing, GOV.UK says to ask the contractor for it, or for a replacement if you've lost it. If you can't get it, you can write to HMRC (PT Operations, HM Revenue and Customs, BX9 1BX) with your name, address and UTR, the contractor's details, the payment dates and why you don't have the statement. The get paid page has the full list.
Step 2: Write down four figures from each statement
Every statement should show these (from HMRC's CIS 340 guide, paragraphs 3.15 and 3.19):
- the gross amount paid to you
- the cost of materials that reduced the amount the deduction was worked out on
- the amount liable to deduction
- the amount deducted
A simple way to keep it straight is one row per statement:
| Contractor | Tax month ending | Gross | Materials | Liable to deduction | Deducted |
|---|
Step 3: Check each row adds up
Two quick checks catch most misread or mistyped figures:
- Gross minus materials should equal the amount liable to deduction. (VAT isn't part of the gross figure if you're VAT registered.)
- The amount deducted should be 20% of the amount liable if you're registered and the contractor could verify you, or 30% if you're not registered or they couldn't verify you.
If a statement doesn't pass, ask the contractor before you rely on it. GOV.UK says to raise it with them if the figures look wrong.
Step 4: Total the year
Add up the gross column and the deducted column across every contractor and every month in the tax year.
Worked example (round numbers)
Sam works for two contractors in the 2025–26 tax year.
| Contractor | Statements | Gross | Materials | Liable | Deducted at 20% |
|---|---|---|---|---|---|
| Contractor A | 12 | £24,000 | £3,000 | £21,000 | £4,200 |
| Contractor B | 4 | £6,000 | £1,000 | £5,000 | £1,000 |
| Total | 16 | £30,000 | £4,000 | £26,000 | £5,200 |
Sam's two totals are £30,000 of pay before deductions and £5,200 of CIS deductions. HMRC uses the return to work out what Sam owes and takes off the £5,200. Whether that leaves a refund depends on the rest of Sam's return: other income, allowable expenses and so on. That part is between Sam, HMRC and anyone Sam asks for advice.
Common mistakes
- Mixing tax years. A payment on 3 April belongs to the tax month ending 5 April, so it's in the old tax year. A payment on 7 April is in the new one.
- Counting a statement twice. It's easy to download the same month twice from a contractor portal.
- Missing a month. Twelve statements a year from each contractor are hard to track by eye. Count them per contractor, for the months you were paid.
- Typing errors. One slipped digit in a deduction changes your claim. Recheck any total you typed by hand.
GOV.UK also says to keep your monthly statements. HMRC may ask for evidence of your deductions when you claim them back.
Limited companies are different
If you work through your own limited company, you don't claim CIS deductions on a Self Assessment return. GOV.UK says the company reports them through its payroll (the Employer Payment Summary) instead. See pay tax and claim back deductions.
FAQ
Is there a single end-of-year CIS statement? GOV.UK describes monthly statements from each contractor, not a yearly one, so you total the monthly statements yourself.
What if I stopped trading part way through the year? GOV.UK says you may be able to claim back deductions already paid that tax year using form CIS40 (sole traders) or CIS41 (partners).
Can I claim my expenses as well? Self-employed people can deduct allowable expenses when working out their profit. GOV.UK's expenses if you're self-employed guide explains what counts. What applies to you is a question for HMRC or an accountant.
Adding up a pile of statements
If you have a folder of PDFs or photos of statements, cissplit does steps 2 to 4. It reads each statement, checks the deduction rate on every one and flags an amount liable that's more than gross minus materials. Then it gives you the year's totals, with every statement listed by contractor and tax month, and flags gaps between a contractor's months. Your first 3 statements are free, and there's no sign-up. You still check the figures against your statements.
This isn't tax advice. Check GOV.UK's CIS guidance for subcontractors or an accountant for your situation, and check the figures before you submit anything.