CIS deductions are eating your cash flow, and your quotes are the reason

The Construction Industry Scheme (CIS) is a UK tax framework under which a contractor must deduct either 20% - for CIS-registered subcontractors - or 30% - for unregistered ones - from each payment made to a subcontractor, but only from the labour element of the invoice. Materials, plant hire, and consumables purchased for the job are excluded before the rate is applied. The deduction does not reduce a subcontractor's taxable profit: it is an advance tax payment, eventually recoverable through Self Assessment or a company's monthly PAYE scheme. What it reduces is cash available in the business right now. A subcontractor with £200,000 of annual construction turnover at the standard 20% rate has £40,000 withheld and sitting with HMRC throughout the year. The problem is not that the money is gone - it is that most subcontractors are pricing and invoicing their work as though they will receive it.

When the quote does not separate labour from materials

Most subcontractors know, in theory, that CIS applies only to labour. In practice, many send a single lump-sum invoice - "supply and fit: £X" - that makes no distinction between the labour and materials content. The contractor receiving that invoice faces a compliance obligation: they must deduct CIS from the labour element, and with no breakdown on the invoice they either apply the deduction to the full amount or make their own conservative estimate of the labour split. Either outcome costs the subcontractor money.

The numbers are concrete. If a subcontractor invoices £2,000 for a job with £600 of materials, CIS at 20% applies to the £1,400 labour portion only - a deduction of £280. Without a materials breakdown, the contractor applies CIS to the full £2,000, deducting £400 instead. That is £120 more withheld than necessary - money the subcontractor will not see until they file their tax return, which for a sole trader can be anywhere from a few months to nearly a year later.

But the lump-sum problem starts earlier than the invoice. It starts at the quote. If the quote presents a single-line price for the job, there is no structure from which to build a correctly split invoice later. When the job completes, someone has to reconstruct from memory what the labour content was. That reconstruction tends to be conservative - meaning more tax withheld than necessary - and the discrepancy between what was quoted and what appears on the invoice can trigger queries that slow payment further.

How the cash drag compounds over a year

Consider a registered subcontractor - an electrical contractor, say - turning over £400,000 in a year with a roughly equal split between labour and materials. CIS applies to the £200,000 labour portion: £40,000 deducted at source across twelve months. For a sole trader, that money is not recoverable until the Self Assessment return is filed after 5 April. File promptly and the refund may arrive within a few months. File at the January deadline and it can be nine or ten months after the first deduction before the cash comes back.

For limited companies the mechanism is faster. CIS deductions are offset against monthly PAYE and National Insurance liabilities via the Employer Payment Summary (EPS), reducing or eliminating what the company owes HMRC each month. But it requires the EPS to be filed on time every month. Miss a filing and the offset does not register, the credit accumulates, and it has to be claimed from HMRC separately.

What amplifies the problem is that many subcontractors absorb it as background noise. The 20% deduction becomes an accepted feature of CIS rather than a cash position they actively manage. When turnover rises - a new framework, a larger contractor relationship, more concurrent projects - the deduction rises in proportion. A business that was comfortable at £200,000 turnover can find itself with £40,000 or more tied up with HMRC at £400,000 turnover, with no change in its payment terms or overhead. The business is busier and shorter of cash simultaneously.

Fixing the structure at quote stage

The practical answer is to treat every CIS job the way the scheme itself treats it: labour and materials are two different line types, priced and tracked separately from the first entry in the quote. When a quote carries a visible labour subtotal and a visible materials subtotal, the estimator has to make an explicit decision about what each element costs and what margin it needs to carry. That discipline catches under-pricing of labour - the most common quoting failure on CIS work - before it is locked in.

It also makes the invoice straightforward. When the quote separates labour from materials and the invoice mirrors that structure, the contractor has everything they need to handle CIS correctly. They exclude the materials amount before applying the rate, deduct the right amount, and pay the correct net figure. No excess deduction, no wait for a refund on money that should never have been withheld, no invoice query because the breakdown does not match the tender.

Mark-up on materials is a related issue. CIS covers only the purchase cost of materials, not the margin on them. A subcontractor who buries the material margin in a blended rate risks a mismatch between what they invoiced for materials and what the contractor will exclude before deducting. Price the margin explicitly so the invoice reflects what the contractor expects to see.

Invoicing in the same structure as the quote

An invoice that mirrors the quote - the same labour lines, the same material lines, with matching figures - gives the contractor everything they need to handle the CIS deduction correctly and settle fast. An invoice that collapses everything into a single total creates friction: the contractor has to make estimates or protect themselves by applying a conservative materials split that costs the subcontractor more than is necessary.

For construction businesses doing regular CIS work, Zigaflow's quotes and invoices share the same line structure. A quote accepted by the customer converts directly into an invoice without re-entry, so the labour and materials breakdown agreed at tender appears on the invoice exactly as it was priced. There is no reconstruction, no inconsistency between what was quoted and what was invoiced, and no room for a lump sum to appear where the contractor needed a clear breakdown.

That consistency matters across every job in a year. A business winning twelve CIS contracts a year at £30,000 each - half labour, half materials - is invoicing £180,000 in labour annually. If lump-sum invoicing causes the contractor to apply CIS to material costs that should have been excluded, the excess deduction is recoverable but only after a wait. That is a cash-flow problem that started at the quote stage.

CIS deductions are not a payroll task for the accountant at year-end. They are a quoting and invoicing discipline. Pricing labour and materials separately from the first line of the quote, carrying that structure through to the invoice, and checking that the contractor's payment statement matches what was invoiced: these habits let CIS work as it is supposed to - an advance against future tax, not a rolling drain on working capital.

Sources

• CIS Deductions Suffered - How Subcontractors Reclaim Their CIS Tax (2026)Trade2Base · accessed 2026-09-30
• CIS Guide 2026 | Rates, Deadlines & Gross Payment StatusKG Business · accessed 2026-09-30
• CIS Materials vs Labour on Invoices: How Deductions ApplyFinistry · accessed 2026-09-30