Why CIS is not just a checkbox on a generalist's return
Most accountants can open a CIS income row in their software and file a self assessment return. That is not the same as being a CIS specialist. The Construction Industry Scheme has enough moving parts that the gap between a competent generalist and a genuine specialist often translates directly into money left unclaimed.
The most obvious example is the deduction base itself. CIS deductions apply to the labour element of a payment only. The cost of materials a subcontractor buys for a job is excluded from the deduction base. So a £1,000 invoice made up of £600 labour and £400 materials has 20% applied to £600, not to the full £1,000. Every page of CIS income a subcontractor earns should be checked against this rule. Generalists who are not in the scheme daily sometimes apply the deduction to the gross payment, which means the over-deduction figure looks smaller than it is and the refund claim is filed short. For a subcontractor earning £50,000 in labour with £15,000 in rechargeable materials, the difference between a correct and an incorrect deduction base is around £3,000 in a single year.
For a plain overview of how the scheme works, the What is CIS guide covers the full scheme mechanics in one place.
The five things a CIS specialist does that a generalist typically does not
1. CIS tax refund claims
Because CIS deductions are taken before any allowances or expenses are counted, most registered subcontractors overpay across the year and are owed a refund. The typical range is £2,000 to £3,000 a year (Dearne Accountancy reports an average first-year client refund of £1,840; RIFT Refunds uses the £2,000 to £3,000 range in their marketing). These are illustrative market figures, not a promise for any individual, but they reflect a genuine structural feature of the scheme: 20% taken at source on labour payments, before tool purchases, vehicle costs, insurance, protective clothing and other allowable expenses are counted, consistently produces an overpayment for most trades.
A specialist builds the refund calculation correctly: gross CIS income, labour versus materials split, all allowable expenses, personal allowance, and any PAYE income from other sources. A generalist may handle the self assessment form accurately without ever asking the question that drives the result: have we accounted for every expense category specific to your trade?
The CIS refund service page covers how the refund process works in practice and what a typical claim involves.
2. Gross Payment Status applications and maintenance
Gross Payment Status (GPS) is the 0% deduction tier. A subcontractor with GPS is paid in full on every invoice, settling tax through self assessment or corporation tax rather than suffering deductions upfront. For a sole trader earning £80,000 in labour in a year, GPS means receiving £80,000 rather than £64,000 across twelve months. The cash-flow difference is substantial.
To qualify for GPS you must pass three tests, all of which must be met:
| Test | What it requires |
|---|---|
| Business test | Carries out construction work in the UK, running through a bank account |
| Turnover test | Net annual CIS turnover of £30,000 (sole trader); £30,000 per partner or £100,000 total (partnership); £30,000 per director or £100,000 total (limited company). Net means excluding VAT and materials. |
| Compliance test | All tax obligations met on time for the past 12 months: no late self assessment returns, no overdue tax, no PAYE defaults |
The compliance test is where applicants most commonly fail, and it is where an accountant's ongoing work pays off. If your returns are always filed on time and your tax account is clean, the compliance test is met automatically. If you have drifted into late filing or an outstanding liability, an accountant can often bring the position into compliance before the 12-month window expires and then time the application correctly.
Since 6 April 2026, maintaining GPS has also become more demanding. Under Finance Act 2026, HMRC can revoke GPS immediately where a contractor knew or should have known about fraudulent connections in the supply chain. The "should have known" standard means a failure to carry out due diligence is enough for revocation, with no intent required. The reapplication ban on fraud grounds is now five years, up from one year previously. For a contractor earning £500,000 a year, losing GPS means £100,000 a year in additional deductions until GPS can be reapplied for. New FA 2004 sections 62A and 62B also add a 20% penalty on anyone who pays or makes a return knowing a connected party deliberately failed to comply, and where the payer is a company HMRC can pursue the responsible directors personally under the existing officer-liability rules.
A CIS specialist manages the three due-diligence steps that protect GPS: re-verifying each subcontractor's CIS status before payment, running a Companies House legitimacy check, and carrying out bank account name verification. A generalist accountant is unlikely to have these processes built into their workflow.
The Gross Payment Status service covers the full application and maintenance process.
3. CIS300 contractor compliance
For clients who are contractors (paying subcontractors, not just receiving payments), a CIS specialist handles the monthly CIS300 return cycle. The return must be filed by the 19th of the following tax month. Payment of deducted CIS to HMRC is due by the 22nd (electronic) or the 19th (cheque).
From April 2026 contractors must also file a nil return for any month in which they made no payments to subcontractors. This obligation was removed in 2015 and reinstated from 6 April 2026. Missing a nil return triggers a £100 penalty on day one, rising to £200 at two months, then £300 or 5% of the CIS liability at six months. A specialist who manages the full return cycle, including nil months, prevents these penalties accumulating.
The return cycle also includes verifying each subcontractor's status with HMRC before payment, which sets the correct deduction rate (0%, 20% or 30%) and, since April 2026, satisfies part of the due-diligence duty that protects GPS under the new anti-fraud rules. A specialist joins these two obligations: the filing obligation and the risk-management obligation, from a single workflow.
4. Domestic reverse charge (DRC)
The VAT domestic reverse charge for construction services has been in force since March 2021. Under the DRC, it is the customer, not the supplier, who accounts for VAT to HMRC. The DRC applies when all five of these conditions are met: the supply is a specified CIS service; both supplier and customer are VAT-registered; both are CIS-registered; the customer is not the end user (they will sell the services on); and the supply is standard-rated or reduced-rated (new-build housing is zero-rated and sits outside the DRC).
The most common source of error is the end-user exception. A property owner, tenant, or developer building for their own use is an end user, which means normal VAT rules apply to any supply made to them. The reverse charge is widely misunderstood and frequently applied incorrectly to end-user contracts, or missed on sub-contractor chains. An incorrect DRC treatment creates VAT underpayments (and potential penalties) or incorrect cashflow modelling for the contractor.
A specialist accountant applies the five-condition test correctly to each supply, identifies end-user situations, and drafts compliant invoice wording. A generalist who encounters a DRC invoice without this background may simply pass it through without checking whether the conditions are actually met.
5. MTD and the gross-income nuance
Making Tax Digital for Income Tax applies to sole traders and partnerships with annual income over £50,000 from April 2026, dropping to £30,000 from April 2027. The obligation is quarterly digital reporting via MTD-compatible software.
The nuance that catches CIS subcontractors out is that the MTD threshold is tested on gross income, not on the net amount received after CIS deductions. A subcontractor who earns £60,000 gross but receives £48,000 after 20% deductions is tested on the £60,000 figure and is in scope from April 2026, even though their bank account shows receipts that look like £48,000. Most generic MTD guides do not explain this. A CIS specialist identifies whether their construction clients are in scope, sets up compliant software, and manages the quarterly submissions, with the grace period for 2026/27 (HMRC will not issue penalty points for late quarterly updates in year one, though late annual returns and late payment penalties still apply) giving a limited window to get set up.
When DIY is reasonable, and when it costs you
There is no rule that says every CIS subcontractor needs an accountant. The question is whether the cost of doing it yourself exceeds the cost of professional help, financially and in time.
Self-filing is reasonable if you are a sole trader with a single source of straightforward CIS income, no employees, no company structure, and modest expenses. You submit a self assessment return, declare gross CIS income, claim the standard expense categories, and HMRC calculates the refund. Many first-year subcontractors do this without difficulty.
A specialist starts to pay for itself in any of the following situations:
- Your refund is significant. On typical first-year figures of £2,000 to £3,000 owed back, the cost of a specialist (who charges £80 to £150 a month for a full-service sole trader package, or perhaps a one-off return fee) is recovered within the first filing. A correct refund that includes all trade-specific expenses (tools, van costs at 55p per mile from April 2026, protective equipment, professional subscriptions) will consistently beat a self-filed return that misses categories.
- You want to apply for Gross Payment Status. The application process, timing the 12-month compliance window, and managing the ongoing due-diligence obligations are not straightforward. An error that disqualifies a GPS application or, worse, results in revocation under the new anti-fraud rules, costs far more than the accountant's fee.
- You run a limited company. The EPS submission route for reclaiming CIS deductions in real time requires accurate monthly payroll and CIS bookkeeping. The difference between using EPS correctly and waiting 18 months for a corporation tax refund on the same money is a material cashflow advantage, and getting EPS submissions wrong creates PAYE/CIS compliance problems.
- You are a contractor as well as a subcontractor. Firms that both receive CIS deductions and pay them to their own subcontractors have a full compliance burden on both sides: CIS300 monthly returns, subcontractor verification, nil returns, and their own refund or EPS position. This is the scenario where the cost of errors is highest and the value of a specialist is most obvious.
- Your income crosses the MTD threshold. If your gross receipts in construction exceed £50,000 in 2026/27, quarterly MTD submissions are now a legal obligation, not an option. Setting up compliant software and managing the quarterly cycle is not complex, but missing the obligation carries late-filing penalties.
What it costs: fee benchmarks
The table below sets out typical monthly fee ranges for CIS-specialist accountancy services in the UK. These are market benchmarks based on sector pricing data and should not be treated as fixed prices for any individual firm (HP §13, for content not guaranteed).
| Service level | Who it suits | Typical monthly fee |
|---|---|---|
| CIS return only | Sole trader, straightforward income, filing self assessment and CIS data only | £20 to £50 per month |
| Full-service sole trader | Sole trader who wants self assessment, expenses review, refund claim, bookkeeping and tax planning | £80 to £150 per month |
| Limited company full service | Company director with CIS income, payroll, corporation tax, annual accounts, EPS submissions, VAT (if registered) | £150 to £250+ per month |
One way to frame the cost decision: a sole trader on a full-service package at £100 a month pays £1,200 a year. On typical figures of £2,000 to £3,000 owed back (illustrative, not guaranteed), the first refund alone covers the annual fee. The real gain, though, is the difference between what a specialist recovers and what you would recover yourself: a specialist who identifies every trade-specific expense category (tools, van costs at 55p per mile, protective equipment) typically recovers several hundred pounds more than a self-filed return would, on top of the compliance protection and the GPS option being kept open.
How to choose a CIS accountant
The how-to-choose questions worth asking before engaging a firm follow from what a genuine specialist does versus what a generalist offers.
Do they file CIS300 monthly returns in-house? Some general accountants outsource CIS300 compliance or do not handle it at all. If you are a contractor, or if you expect to become one, a firm that manages the full monthly cycle is essential, not a nice-to-have.
Have they managed GPS applications and maintained GPS status for construction clients? GPS applications fail on the compliance test more often than on turnover. A firm that has run the process for multiple clients will know how to prepare the ground correctly. Since April 2026 the maintenance obligation is also more demanding, so experience with the new anti-fraud regime matters.
How do they handle EPS submissions for limited company clients? If you operate through a company and have CIS deducted by contractors, in-month EPS submissions are the mechanism for recovering those deductions against your PAYE liability. A firm that handles this monthly gives you a cashflow advantage worth having. Ask whether they run these submissions in-house or rely on you to manage the bookkeeping.
Are they set up for MTD-compatible quarterly reporting? From 2026/27 this is a compliance obligation for sole traders with gross construction income over £50,000. The MTD grace period for 2026/27 (no penalty points for late quarterly updates in year one) gives a window to get set up, but the annual return and payment obligations still apply in full. A firm that has already onboarded construction clients onto MTD-compatible software is ahead of one that is still preparing.
What does the monthly fee include? The range from £20 to £250+ a month covers very different service levels. Clarity on what is included (and what triggers an additional charge) prevents surprises. A transparent specialist will set out in writing what the monthly fee covers: self assessment, quarterly MTD updates, CIS300 returns, GPS maintenance, EPS submissions, or any combination of these.
If your first question is what you might be owed, start with our CIS refund estimator. Two minutes with your deduction statements gives you a working figure before you speak to anyone.
The faceless brand rule means a guide like this cannot rank accountants or compare named firms. What it can do is direct you to where a specialist conversation starts. Our CIS accounting services page sets out the full range of what a construction-specialist firm does, so you can judge whether the scope matches what your situation needs. For construction-sector compliance that goes beyond a generalist's tick-box, the gap between specialist and general practice is rarely academic.