Construction tax: the deductions and reliefs that decide what a contractor keeps
In short
UK construction businesses lose margin to CIS deductions, the VAT domestic reverse charge, and incomplete job cost records - not to pricing decisions alone. Split labour from materials on every invoice and treat job cost records as a pricing input, not a tax afterthought.
Construction businesses face CIS deductions, the VAT domestic reverse charge, and corporation tax obligations on every job. The margin hit comes not from the rates themselves but from treating tax handling as paperwork rather than as part of how jobs are priced and costed.
A UK construction business deals with at least three distinct tax obligations on every job it prices and runs: the Construction Industry Scheme (CIS), the VAT domestic reverse charge, and corporation tax or income tax on its own profits. Each one bites at a different point in the job cycle. CIS bites at the invoice, reducing the cash a subcontractor receives before the job is even closed out. The domestic reverse charge bites at the VAT return, removing a float that many smaller contractors had quietly been using as working capital. Corporation tax bites at year end, but the size of the bill is shaped by decisions made job by job - what costs were documented, what allowances were claimed, and how accurately the labour split was recorded. The contractors who lose least to these obligations are not the ones with the best accountants. They are the ones who treat tax handling as part of how a job is run, not something that happens to it afterwards.
CIS deductions: the labour split is where the money goes
CIS rates for the 2026/27 tax year are unchanged: 0% for subcontractors with gross payment status, 20% for those registered with HMRC, and 30% for those who are unregistered or whose details HMRC cannot match. These rates apply only to the labour element of an invoice - not to materials, VAT, plant hire, or consumables, provided those items are shown separately.
That last clause is where most invoices fail. A bundled figure - "Groundworks, £3,500" with no line-item split - gives the contractor's accounts team no choice but to apply the deduction to the whole amount. The deduction should come off the labour portion; instead, it comes off everything. The subcontractor has effectively handed HMRC a portion of their materials cost and will wait until they file their Self Assessment or Employer Payment Summary to get it back. On a £3,500 invoice where labour is £2,400 and materials are £960, the difference between a correctly split invoice and a bundled one is £192 sitting with HMRC instead of in the subcontractor's account. Multiply that across a year's volume and the number is not trivial.
The 30% rate causes a different but equally preventable problem. On £60,000 of annual labour, the gap between the registered 20% rate and the unregistered 30% rate is £6,000 of working capital withheld for months. Registering for CIS as a subcontractor costs nothing and takes under an hour. The compliance test for gross payment status - which eliminates deductions entirely - is stricter, requiring a clean 12-month compliance record, a UK business bank account, and construction turnover of at least £30,000 excluding VAT and materials. One late Self Assessment payment in the previous 12 months can prevent approval. That status is now more fragile than it was: from 6 April 2026, HMRC can cancel gross payment status immediately, without advance notice, where it suspects a connection to fraudulent tax evasion, and bar reapplication for five years. Businesses holding gross payment status need to treat their compliance record as a balance-sheet item, not an administrative afterthought.
Split every invoice line
Subcontractors should list labour, materials, and plant hire as separate lines on every invoice. It takes two minutes and prevents the contractor's accounts team from applying the CIS deduction to costs that are legally excluded.
The domestic reverse charge: a working capital shift, not just a compliance rule
The VAT domestic reverse charge for construction has applied since March 2021. Where both parties are VAT-registered, the work falls under CIS, and the customer is not an end user, the subcontractor does not charge VAT. Instead, the contractor accounts for the VAT on their own return - both as output and input tax, which typically nets to zero for a fully VAT-registered business.
That netting-to-zero is the important phrase. The reverse charge rarely creates a net VAT cost for the main contractor. But it does mean the subcontractor never collects VAT on those invoices at all. For subcontractors who had been using the quarterly VAT float as short-term working capital - paying for materials before the VAT quarter closed, then using the incoming VAT to cover the gap - the reverse charge removed that cushion entirely. The cash flow effect was real and immediate.
From 6 April 2026, local authority payments are fully exempt from the reverse charge. Standard VAT rules now apply to those invoices. For contractors working in the public sector, that changes how those invoices need to be set up. Applying the reverse charge to a local authority payment after April 2026 is incorrect, and the error flows through to both parties' VAT returns.
End user status matters
The reverse charge does not apply if the customer is an end user - typically a business that will use the building for its own purposes rather than for onward supply. Always confirm end user status before issuing an invoice. Getting this wrong in either direction creates a VAT error that both parties will need to correct.
What job-level cost records actually need to capture
Tax handling loses money on construction jobs not because the rates are high but because the records feeding the calculation are incomplete. CIS is calculated on what the invoice says. Corporation tax is calculated on what the accounts say. If neither reflects what the job actually cost - in materials, in plant, in labour hours - the business is either overpaying tax or underpricing future work.
The Annual Investment Allowance lets most businesses deduct plant and machinery costs in the year of purchase rather than spread them over many years. For a contractor buying a van, a generator, or site equipment, that is a same-year reduction in taxable profit. Missing it because the purchase was not coded to the right cost category is money left on the table. The Structures and Buildings Allowance provides a smaller annual rate of relief on qualifying construction costs for new commercial buildings - modest in any single year, but claimable over decades. More importantly, identifying which elements within a structure qualify as plant and machinery rather than structural costs can shift expenditure into a higher rate of immediate relief. The paperwork that makes that distinction possible is done at the point of purchase order, not at year end.
Job records that capture cost categories accurately - labour versus materials versus plant hire, each coded correctly when the purchase order is raised - do two things simultaneously. They give the accounts team what they need to produce an accurate tax position without guesswork, and they give the business the cost data to price the next comparable job correctly. These are not separate benefits. A business that treats job cost records as a tax compliance exercise learns what jobs actually cost; a business that treats them as an invoicing formality does not.
Zigaflow's job costing tools let contractors record costs against a job as purchase orders are raised, so the cost-versus-quoted split is visible before the invoice is raised - not after the year-end reconciliation. That real-time view is what separates a business that can price confidently from one that finds out how the job performed after it has already been priced again.
Pricing that ignores tax handling is incomplete
A quote built on direct labour and material costs, with tax handling treated as a separate accounting problem, is not a complete quote. It is a quote with a hidden deduction the business will absorb later.
A subcontractor pricing a job needs to know whether they are on a 20% or 30% CIS rate for that contractor, whether the reverse charge applies, and whether their materials split is clearly documented. A contractor pricing a job that includes sub-labour needs to know what CIS obligations will fall on them and whether those costs have been factored into the programme. None of this requires a tax adviser on every quote. It requires the job record to carry the right information and the invoice to be issued in a format that makes the deduction basis unambiguous.
The construction industry businesses that manage this well are not those with the most sophisticated tax arrangements. They are those with the tightest connection between what a job costs on the ground and what the invoices say. That connection is maintained job by job, not at year end. The tax saving is a consequence of accurate operations, not a separate exercise.
Sources
- Construction Industry Scheme: a guide for contractors and subcontractors (CIS 340)HMRC / GOV.UK · accessed 2026-10-14
- CIS Tax Deduction Explained: 20% or 30%?BuildByJai · accessed 2026-10-14
- Construction Industry Scheme (CIS): How it worksBDO · accessed 2026-10-14
- Construction Industry Scheme (CIS) Guide 2026/27Accounting People · accessed 2026-10-14