Your No-Nonsense Guide to Filing a CIS Return
“I needed some advice and help with an urgent matter. I phoned several people who said they could not do it. David answered the phone and said no problem at all. Everything was done in 24 hours. I highly recommend STZ Accounting.”
If you are a subcontractor in the UK construction industry, CIS deductions are coming out of your pay every month and you may be owed money back. This guide explains exactly what a CIS return is, what happens if you fall behind, and how to get it sorted quickly.
Why CIS returns matter for subcontractors
The Construction Industry Scheme (CIS) sets the rules for how contractors must handle payments to subcontractors for construction work across the UK. Under the scheme, contractors deduct tax at source before they pay you, and those deductions are tracked through monthly returns. If your CIS paperwork is not in order, you can end up overpaying tax and waiting a long time to get it back.
As a subcontractor, registering with HMRC for CIS means your contractor deducts tax at the standard 20% rate rather than the higher 30% rate applied to unregistered subcontractors. That difference adds up fast across a full year of work. Getting your CIS position straight is one of the quickest ways to stop losing money to HMRC unnecessarily.
From 6 April 2026, HMRC has reinstated the requirement for mainstream contractors to file a nil return in any month where no subcontractors were paid. Missing a nil return counts as a late filing and can trigger a penalty. See the updated CIS 340 guidance for the full rules.
Where most subcontractors go wrong with CIS
Most CIS problems are not caused by deliberate errors. They come from not knowing the rules, missing a deadline while you are flat out on site, or assuming your contractor is handling everything on your behalf. According to Accountax Zone, common CIS errors include applying the wrong deduction rate, having incorrect subcontractor details on file, and submitting late returns. Penalties for these errors can reach up to £3,000.
Filing late or missing returns entirely
CIS monthly returns must be submitted by the 19th of each month following the tax month they cover. A single missed deadline triggers a penalty, and penalties increase the longer the return stays unfiled. If you have returns outstanding going back several months, the total exposure can be significant before you have realised there is a problem.
Assuming your contractor is handling it
Contractors file their own monthly CIS returns showing what they paid you and what they deducted. But that does not mean your own tax position is correct or that you are claiming back everything you are owed. Your self assessment tax return is where you recover overpaid CIS deductions, and that is entirely your responsibility, not your contractor’s.
“Most of the subcontractors I work with are not in trouble with HMRC because of anything serious. They have just been too busy to sort the paperwork and it has built up. We get it filed, claim back what they are owed, and that is usually the end of it.”
What to do with your CIS return, step by step
The process for getting your CIS position in order follows a clear sequence. Whether you are up to date or months behind, the same steps apply. Working through them in order will show you exactly where you stand and what needs to be filed.
- Gather your CIS deduction statements. Your contractor must give you a CIS statement for every month they deduct tax from your pay. Collect these statements for the current tax year. If you are missing any, contact your contractor to request copies.
- Check your HMRC registration status. Log into your HMRC account or ask your accountant to check whether you are registered as a CIS subcontractor. If you are not registered, your contractor may be deducting at the higher 30% rate. Registering brings that down to 20% going forward.
- Include your CIS deductions in your self assessment tax return. The total CIS tax deducted during the year is offset against your income tax bill when you file your self assessment return. If your deductions exceed what you owe, HMRC refunds the difference. A qualified accountant can calculate this and file on your behalf.
If you have returns that are late or have never been filed, the approach is the same but time matters more. Late returns accumulate penalties, so getting them submitted as quickly as possible limits the damage. An accountant who handles CIS work regularly can move fast on overdue returns and deal with HMRC directly if needed.
What it costs and what to expect
The cost of sorting your CIS position depends on how far behind you are and whether your records are in reasonable order. A one-off CIS catch-up and self assessment filing is typically a fixed-fee job. At STZ Accounting, David works to agreed fixed prices with no surprise additions at the end. There are no hourly rates and no vague quotes that balloon once work begins.
| Option | Pros | Cons |
|---|---|---|
| Do it yourself | No accountant fee | High risk of applying wrong deduction rates, missing CIS statements, or filing late and triggering penalties up to £3,000 |
| Use an accountant | Accurate filing, correct refund claimed, HMRC correspondence handled for you | Accountant fee applies, though a fixed quote means you know the cost upfront |
How to get your CIS sorted today
If your CIS returns are behind or you are not sure whether you have been claiming back everything you are owed, the first step is a short conversation to look at your situation. David offers a free introductory call where he will tell you plainly what needs to be done, what it will cost, and how long it will take. There is no obligation and no paperwork to fill in before the call.
- Locate your CIS deduction statements from your contractor for the current and any previous tax years where returns may be outstanding.
- Book a free call with David at STZ Accounting using the link below. Bring your statements to the call and he will confirm your position and give you a fixed quote on the spot.
Ready to sort your CIS returns?
David will file your outstanding CIS returns and self assessment, claim back any overpaid deductions, and deal with HMRC on your behalf. Fixed fee, no tie-in, same-day responses.
Is your CIS position costing you money?
Answer five quick questions and find out whether you are owed a refund or have returns that need filing.
AAT qualified accountant based in Strathaven. Personal, one-to-one accounting for small businesses and sole traders across the UK.