Self Assessment for CIS subcontractors: your step-by-step 2026/27 guide
If you've got CIS taken off your pay, a Self Assessment return is how that money gets reconciled. For most subbies, it ends in a refund.
By Bobby Gardiner·13 July 2026·6 min read
- Under CIS, contractors stop 20% (if you're registered) or 30% (if you're not) from your labour and hand it to HMRC before you see a penny.
- Those deductions take no account of your personal allowance or expenses, so most subcontractors are due a refund rather than a bill.
- You'll need a UTR and to be registered for Self Assessment. The online filing deadline is 31 January.
- Hold on to your monthly CIS statements and expense records. If statements go missing, they can be rebuilt from your bank.
- Refunds usually land around two weeks after filing, paid straight to you. Never through us, and never as a cut of your money.
- From April 2026, Making Tax Digital applies to subbies whose gross self-employment income (your turnover, before expenses) tops £50,000.
If you work on the tools and have tax stopped before you're paid, you're inside the Construction Industry Scheme (CIS). That means a Self Assessment tax return every year. It sounds like a chore, but for most subbies it's the moment the money comes back.
The bit hardly anyone explains on site is this. CIS deductions take no account of your personal allowance or your expenses, so the tax stopped from your labour is almost always more than you owe. Your return is how you claim the difference back.
This guide runs through the lot in plain English: what CIS is, why you're probably owed a refund, what to get together, the deadlines that count for the 2026/27 tax year, and how the money reaches your account. No jargon and no scare tactics.
What CIS is and why you're in it
The Construction Industry Scheme is how HMRC collects tax from construction work at source. If you're a subcontractor, the contractor paying you has to take a slice off your labour and send it to HMRC on your behalf.
Registered for CIS, they take 20%. Not registered, it jumps to 30%, which is reason enough to sort your registration. Either way you're still self-employed, a sole trader running your own show and responsible for your own tax return.
This is the part that trips people up. The deduction isn't your final tax bill; it's an advance payment against it. Your Self Assessment return is where the whole thing gets squared up.
- Registered subbie: 20% deducted from labour
- Unregistered subbie: 30% deducted from labour
- Deductions apply to labour only, not materials
- You remain self-employed and must file a Self Assessment return each year
Why most subbies get money back
This is the good news. When a contractor stops CIS, they take no account of your personal allowance (the slice of income you can earn tax-free) or any of your expenses: tools, van, fuel, materials, protective gear, insurance, phone.
So you've overpaid all year without realising. When you file, your real taxable profit gets worked out properly, with the allowance applied and expenses knocked off, and the CIS already taken is credited against that final figure. Nine times out of ten, HMRC ends up owing you.
Fancy a rough idea before you file? Our free CIS refund estimator gives you a ballpark in a couple of minutes. And if you'd sooner someone handled the lot, that's what our CIS accounting service is for.
What you need before you file
Getting organised upfront makes the whole thing painless. This is the checklist.
Missing a few CIS statements is no disaster. If they've been lost, we can rebuild your deductions from your bank records, so a shoebox that's seen better days won't hold you up.
- A UTR (Unique Taxpayer Reference): your 10-digit tax ID, plus registration for Self Assessment
- Your monthly CIS statements: the contractor should hand you one each month showing pay and deductions
- Records of your income: invoices and bank deposits
- Records of your expenses: tools, van, fuel, materials, PPE, phone, insurance, use of home
The 2026/27 deadlines that matter
The tax year runs from 6 April to 5 April. Miss the big dates and HMRC charges penalties, so get these on the calendar.
One extra thing to know. If your tax bill comes to over £1,000 and less than 80% was collected at source, you may have to make payments on account, which are advance instalments towards next year's bill. For most refund-due subbies this won't bite, but it's worth having on your radar.
- 5 October after the tax year you first started working for yourself: a one-off deadline to register for Self Assessment (it only applies in your first year, after that you're already registered)
- 31 October: the deadline for paper returns
- 31 January: the deadline for online returns and any balancing payment due
- Register early, because leaving it late is the most common reason refunds get delayed
Filing your return and getting the refund
You file your Self Assessment return online through HMRC, or you get an accountant to do it for you. The return adds up your income, takes off your expenses, applies your personal allowance and credits the CIS already stopped. If you've overpaid, the balance comes back as your refund.
Once it's filed, refunds usually arrive around two weeks later, paid directly to you, into your own bank account. HMRC runs checks, and the January rush can add a little time, so filing earlier in the year gets your money back sooner.
We charge a fixed fee agreed upfront, never a percentage of your refund. Your refund is yours. It comes to you, not through us. If you'd like a real person to take the whole thing off your plate, get in touch and we'll sort it.
Making Tax Digital, briefly
Making Tax Digital for Income Tax (MTD ITSA) is changing how self-employed people report to HMRC, moving from one annual return to quarterly digital updates.
From April 2026 it applies if your gross self-employment income (your turnover, before expenses) tops £50,000, then over £30,000 from April 2027 and over £20,000 from April 2028. If that's you, there's nothing to fear. It means keeping digital records and sending updates through the year, and that's about it. Our Making Tax Digital guide explains what it means for subcontractors and how we make it seamless.
Let's get your CIS refund sorted
Deal directly with Bobby Gardiner (CAT FMAAT), not a call centre. Fixed fee agreed upfront, your refund paid straight to you, and no nasty surprises. Try the free CIS refund estimator for a ballpark, or get in touch and we'll handle the whole return for you.
Common questions
Do CIS subcontractors have to do a Self Assessment tax return?
Yes. As a CIS subcontractor you're self-employed (a sole trader), so you file a Self Assessment tax return each year. It's how the CIS stopped from your pay gets reconciled against your real tax bill. Because those deductions take no account of your personal allowance or expenses, most subbies end up due a refund rather than owing anything.
How much CIS refund will I get and when?
It depends on your income, your expenses and how much CIS was stopped. Because the 20% (or 30%) taken off takes no account of your tax-free personal allowance or your expenses, most subcontractors are owed money back. Refunds usually arrive around two weeks after filing, paid directly into your own bank account. For a quick ballpark, try our free CIS refund estimator.
What happens if I've lost my CIS statements?
You don't need every piece of paper. If your monthly CIS payment and deduction statements have gone missing, we can rebuild your deductions from your bank records, so lost statements won't stop you filing or claiming your refund.