CIS Accountant: What They Do, What It Costs, and Why Most Subcontractors Need One
The Construction Industry Scheme sits apart from ordinary tax rules in a way that catches out even experienced tradespeople. Deductions come straight off your invoice before you’ve even seen the money, and unless someone’s actively tracking what’s been taken and what you’re owed back, it’s remarkably easy to leave hundreds — sometimes thousands — of pounds sitting unclaimed with HMRC. This is exactly the gap a CIS accountant is built to close.
This guide sets out what a CIS accountant actually does day to day, who genuinely needs one, what the service tends to cost, and why so many subcontractors end up owed a refund without realising it. It’s written from direct experience handling CIS work for contractors and subcontractors across the UK.
Quick Answer
A CIS accountant specialises in the Construction Industry Scheme — the HMRC system that requires contractors to deduct tax from subcontractor payments before they’re paid. They handle CIS registration, monthly contractor returns, subcontractor verification, and Self Assessment filing for subcontractors, and they’re particularly valuable for reclaiming tax that’s been over-deducted throughout the year. While using one isn’t a legal requirement, the scheme’s rules are detailed enough that mistakes routinely cost people money, either through penalties or unclaimed refunds.
Key Takeaways
- CIS deductions are taken at 20% for registered subcontractors, 30% for unregistered ones, or 0% for those with gross payment status.
- Contractors must submit monthly CIS returns to HMRC and verify each subcontractor’s status before paying them.
- Subcontractors frequently overpay tax through CIS deductions and are owed a refund once allowable expenses are properly accounted for.
- A CIS accountant isn’t legally required, but the scheme’s rules are detailed enough that mistakes commonly lead to penalties or lost refunds.
- Gross payment status — which removes deductions entirely — has specific compliance, turnover, and business tests that a specialist can help you meet.
- Typical CIS accountant fees run from roughly £20–£40 a month for basic compliance up to £300+ for a full annual service including refund claims.
Table of Contents
- What Is a CIS Accountant?
- What Does a CIS Accountant Actually Do?
- CIS Deduction Rates Explained
- Monthly CIS Returns: What Contractors Need to File
- Gross Payment Status: What It Is and Who Qualifies
- Do You Actually Need a CIS Accountant?
- How Much Does a CIS Accountant Cost?
- Why Subcontractors Often End Up Owed a Refund
- CIS Accountants for London Contractors
- Common Mistakes People Make
- Accountant Insights: What We See in Practice
- Should You Hire a CIS Accountant? (Decision Framework)
- DIY vs CIS Accountant (Comparison)
- Checklists
- FAQs
- Sources
- Final Thoughts
What Is a CIS Accountant?
A CIS accountant is someone who specialises in the Construction Industry Scheme — the framework HMRC set up to govern how contractors pay subcontractors for construction work. The scheme covers most work on permanent or temporary buildings and structures, along with civil engineering projects like roads and bridges, and it requires contractors to deduct tax directly from a subcontractor’s payment before the money ever reaches them.
Rather than a subcontractor receiving their full invoice value and sorting out tax later, CIS effectively collects tax in advance, similar in spirit to PAYE but applied to self-employed construction workers. A CIS accountant understands both sides of this: the contractor’s obligation to deduct and report correctly, and the subcontractor’s need to track what’s been deducted and reclaim any overpayment.
What Does a CIS Accountant Actually Do?
Depending on whether you’re a contractor, subcontractor, or both, a CIS accountant’s work typically covers:
- CIS registration — getting you set up correctly with HMRC as a contractor or subcontractor from the outset.
- Subcontractor verification — for contractors, checking each subcontractor’s status with HMRC before the first payment, which determines the deduction rate applied.
- Monthly CIS returns — contractors must report deductions to HMRC every month, and late or incorrect returns carry penalties.
- Record-keeping and deduction statements — issuing subcontractors with the paperwork confirming what’s been deducted, which they’ll need for their own tax return.
- Self Assessment filing for subcontractors — pulling together income, CIS deductions already made, and allowable expenses to work out the final tax position.
- Reclaiming overpaid tax — identifying and claiming back CIS deductions that exceed the subcontractor’s actual tax liability once expenses are factored in.
- Gross payment status applications — helping qualifying subcontractors apply to be paid without any deduction at all.
CIS Deduction Rates Explained
How much tax gets taken off a subcontractor’s payment depends entirely on their registration status:
| Status | Deduction Rate | What It Means |
|---|---|---|
| Registered subcontractor | 20% | Standard rate once verified and registered with HMRC under CIS |
| Unregistered subcontractor | 30% | Applied when someone hasn’t registered — a significant, avoidable difference |
| Gross payment status | 0% | No deduction at all; the subcontractor handles their own tax and National Insurance directly |
The gap between 20% and 30% is one of the most common — and most easily fixed — reasons subcontractors lose money unnecessarily. Registering for CIS as soon as you start subcontracting work avoids paying an extra 10% that simply didn’t need to be deducted in the first place.
Monthly CIS Returns: What Contractors Need to File
If you’re a contractor, the monthly CIS return is the core ongoing compliance obligation, and it’s due by the 19th of each month following the tax month it covers. The return needs to show every payment made to subcontractors during that period, the deductions taken, and confirmation that each subcontractor’s employment status has genuinely been considered rather than assumed.
Even a month with no subcontractor payments still requires a nil return to be submitted — HMRC doesn’t treat “nothing to report” as a reason to skip filing. This is one of the more commonly missed obligations among smaller contractors who assume the return is only necessary when payments have actually been made.
Because the return is monthly rather than annual, errors tend to compound quickly if they’re not caught early — a wrong deduction rate applied in April can affect every subsequent month until someone notices, which is exactly the kind of routine but easy-to-miss detail a CIS accountant is built to catch.
Gross Payment Status: What It Is and Who Qualifies
Gross payment status lets a qualifying subcontractor be paid in full, with no CIS deduction taken at all — they then manage their own Income Tax and National Insurance through Self Assessment, much like any other self-employed person outside the scheme. It’s a genuine cash flow advantage, since money isn’t being held back throughout the year waiting to be reclaimed.
To qualify, a business generally needs to pass three tests set by HMRC: a compliance test (a clean recent history of filing and paying taxes on time), a turnover test (construction turnover above a set threshold, excluding materials), and a business test (evidence the business is run through a genuine bank account and carries out construction work in the UK). A CIS accountant can review whether you’re likely to meet these tests before you apply, since a rejected application can be avoided with the right preparation.
Do You Actually Need a CIS Accountant?
There’s no legal requirement to use one — you can register for CIS, file monthly returns, and complete your Self Assessment entirely on your own. In practice, though, a few situations make professional help genuinely worthwhile:
- You’re a contractor managing several subcontractors, where monthly returns and verification checks quickly become time-consuming to track manually.
- You’re a subcontractor who suspects you’re owed a refund but isn’t confident calculating allowable expenses against what’s already been deducted.
- You’re applying for gross payment status and want a realistic assessment of whether you’ll meet the qualifying tests.
- You’ve received a penalty notice for a late or incorrect CIS return and need help resolving it.
- Your record-keeping is inconsistent, making it hard to know exactly what’s been deducted across multiple contractors over the year.
How Much Does a CIS Accountant Cost?
Pricing depends on whether you need ongoing monthly compliance work or a one-off annual service:
| Service | Typical Cost (+ VAT) |
|---|---|
| Monthly CIS return filing (contractors) | £20 – £40 per month, depending on subcontractor numbers |
| Subcontractor Self Assessment including CIS reconciliation | £150 – £300 |
| CIS registration (one-off) | Often free or a small fixed fee, sometimes bundled into a wider package |
| Gross payment status application support | £100 – £250, depending on complexity |
Many accountants bundle subcontractor Self Assessment and CIS reconciliation into a single annual fee, since the two are closely linked — the refund calculation depends entirely on having an accurate year-round record of deductions.
Why Subcontractors Often End Up Owed a Refund
CIS deductions are calculated on the gross value of a subcontractor’s invoice, before any of their business expenses are taken into account. Since tools, equipment, vehicle costs, protective clothing, insurance, and even certain accommodation costs are all allowable against income, the tax actually owed once expenses are deducted is frequently lower than the 20% (or 30%) already taken off throughout the year.
Illustrative Example: A subcontractor earning £35,000 across the year with £8,000 in legitimate expenses (tools, van costs, insurance, protective gear) would have their tax calculated on the £27,000 net figure — yet CIS deductions were taken on the full £35,000 gross amount as it was invoiced. The difference between tax paid via deduction and tax actually owed is the refund due once the Self Assessment return is filed.
This is exactly why keeping organised records of expenses throughout the year — not just at tax return time — makes such a meaningful difference to the size of the refund a subcontractor eventually receives.
CIS Accountants for London Contractors
London’s construction sector — spanning everything from residential extensions to major civil engineering projects — means a large number of subcontractors moving between multiple contractors within a single tax year. Each contractor deducts CIS independently, so a subcontractor working across several London sites can end up with deductions spread across half a dozen different payers, making it easy to lose track of the total picture without proper records.
Contractors managing subcontractor teams across London projects also face a higher administrative load simply due to volume — more subcontractors means more monthly verification checks and a bigger monthly return to get right. A CIS accountant familiar with how London’s construction supply chains typically operate can usually spot deduction discrepancies or missed refund opportunities faster than a general practice unfamiliar with the scheme’s specifics.
Common Mistakes People Make
1. Not registering for CIS before starting subcontract work
Why it happens: New subcontractors sometimes aren’t aware registration exists, or assume it happens automatically.
Consequence: Deductions are taken at 30% instead of 20%, an avoidable extra cost on every payment.
How to avoid it: Register for CIS with HMRC before invoicing your first contractor.
2. Losing track of deduction statements from multiple contractors
Why it happens: Subcontractors working for several contractors receive separate paperwork from each one, which is easy to misplace.
Consequence: An inaccurate or understated refund claim, since HMRC’s figures rely on these being reconciled correctly.
How to avoid it: Keep every CIS deduction statement in one place as it’s received, rather than trying to gather them all at year-end.
3. Not claiming allowable expenses against CIS income
Why it happens: Subcontractors sometimes assume the CIS deduction already accounts for their costs.
Consequence: Overpaying tax throughout the year and missing out on a refund that requires an accurate expense claim to unlock.
How to avoid it: Track tools, vehicle costs, insurance, and protective equipment throughout the year, not just when filing.
4. Missing monthly CIS return deadlines as a contractor
Why it happens: Monthly filing is easy to deprioritise compared to project deadlines.
Consequence: Automatic penalties apply for late CIS returns, which can accumulate quickly across a full tax year.
How to avoid it: Set a fixed monthly reminder, or hand the filing to an accountant who manages it as a routine task.
5. Applying for gross payment status without checking eligibility first
Why it happens: The cash flow benefit is appealing, so some subcontractors apply without reviewing the qualifying tests.
Consequence: A rejected application wastes time and can flag inconsistencies HMRC may look at more closely.
How to avoid it: Have an accountant review your compliance, turnover, and business position against the tests before applying.
Accountant Insights: What We See in Practice
- Subcontractors who track expenses monthly consistently claim larger refunds than those who try to reconstruct a year of costs at tax return time.
- The 20% vs 30% registration gap is one of the easiest wins in construction accounting — it costs nothing to fix and directly increases take-home pay from day one.
- Contractors underestimate how quickly monthly CIS penalties add up once a return is missed — a single missed deadline early in the year can snowball if it isn’t corrected immediately.
- Gross payment status is under-applied for among subcontractors who would likely qualify, often because they assume the process is more complicated than it actually is.
- Vehicle and tool expenses are the most commonly under-claimed costs we see among construction subcontractors, usually because receipts aren’t kept systematically.
Should You Hire a CIS Accountant?
A simple way to decide:
Step 1: Identify your role.
Contractors managing multiple subcontractors generally benefit most from ongoing monthly support; subcontractors benefit most around refund calculation and expense tracking.
Step 2: Assess your current record-keeping.
If deduction statements and expenses are scattered or incomplete, professional help will likely recover more than it costs.
Step 3: Consider gross payment status.
If your turnover and compliance history look strong, it’s worth having a specialist check your eligibility.
Step 4: Weigh the fee against the likely refund or penalty risk.
For most active subcontractors, the refund recovered typically outweighs the cost of the service.
DIY vs CIS Accountant
| Option | Advantages | Disadvantages | Best For |
|---|---|---|---|
| Handle CIS yourself | No fee; full control | Easy to miss expenses; monthly returns are time-consuming for contractors | A single subcontractor with very simple, well-organised records |
| CIS accountant | Maximises refunds; handles monthly compliance; reduces penalty risk | Ongoing or annual fee | Contractors with multiple subcontractors, or subcontractors wanting a larger, accurate refund |
Checklists
Checklist 1: For Subcontractors
- ✓ Confirm you’re registered for CIS (20% rather than 30% deduction)
- ✓ Keep every deduction statement from each contractor
- ✓ Track tools, vehicle, and protective equipment costs throughout the year
- ✓ Check whether you might qualify for gross payment status
- ✓ File your Self Assessment to claim any refund owed
Checklist 2: For Contractors
- ✓ Verify each subcontractor’s status with HMRC before first payment
- ✓ File CIS returns monthly, without exception
- ✓ Issue deduction statements to subcontractors promptly
- ✓ Keep records of all CIS payments and deductions made
- ✓ Review subcontractor status periodically in case it changes
FAQs
What does a CIS accountant do?
They manage CIS registration, monthly contractor returns, subcontractor verification, and Self Assessment filing, with a particular focus on reclaiming overpaid tax for subcontractors.
Do I legally need a CIS accountant?
No, it’s not a legal requirement, but the scheme’s detailed rules mean mistakes commonly lead to penalties or missed refunds.
How much CIS tax is deducted from subcontractors?
20% for registered subcontractors, 30% for unregistered ones, or 0% for those with gross payment status.
Can I claim back overpaid CIS tax?
Yes — most subcontractors reclaim any overpayment through their annual Self Assessment return, once allowable expenses are factored in against deductions already made.
What is gross payment status?
A status that allows a qualifying subcontractor to be paid in full with no CIS deduction, managing their own tax and National Insurance directly instead.
How much does a CIS accountant cost?
Monthly contractor compliance typically runs £20–£40 a month, while subcontractor Self Assessment with CIS reconciliation is usually £150–£300.
What happens if a contractor misses a CIS return deadline?
HMRC applies automatic penalties for late monthly CIS returns, which can increase the longer the return remains outstanding.
What expenses can subcontractors claim against CIS income?
Tools and equipment, vehicle costs, protective clothing, insurance, and certain accommodation costs are commonly allowable, subject to normal expense rules.
Do I need to verify subcontractors as a contractor?
Yes — contractors must verify each subcontractor’s status with HMRC before making the first payment, which determines the deduction rate applied.
Is CIS the same as Self Assessment?
No — CIS is the deduction system applied to payments during the year; Self Assessment is the annual return that reconciles what’s actually owed against what’s already been deducted.
Sources
- HMRC / GOV.UK — Construction Industry Scheme (CIS)
- GOV.UK — CIS: register your business as a contractor or subcontractor
- GOV.UK — Gross payment status and qualifying tests
- ICAEW — Construction Industry Scheme guidance
CIS deduction rates, thresholds, and qualifying tests are set by HMRC and subject to periodic review — always confirm current figures on GOV.UK before publication.
Final Thoughts
The Construction Industry Scheme is one of the areas of UK tax where the gap between doing it yourself and getting specialist help tends to show up directly in your bank balance — through avoidable deductions, missed expenses, or a refund that never gets claimed. Whether you’re a contractor managing monthly compliance or a subcontractor trying to work out what you’re actually owed, the scheme rewards accurate, consistent record-keeping more than almost any other part of UK tax.
If you’re unsure whether you’re paying the right rate, missing eligible expenses, or could qualify for gross payment status, speaking with a CIS accountant can quickly clarify where you stand — and often uncover money that’s already yours.
Written by:
Shamayun Chowdhury
Senior Accountant, Major Accountancy
Lecturer in Accounting, Nottingham Trent University
CIMA Qualified, 15+ Years Experience
Last Reviewed: August 2026