The VAT Flat Rate Scheme Trap for Construction Businesses

We still see subcontractors sitting on the VAT Flat Rate Scheme years after it quietly stopped doing them any good. It made sense once, a single percentage instead of tracking every invoice, a bit of margin baked in if you kept costs low. Then the domestic reverse charge for construction arrived, and for a lot of businesses the maths behind the scheme broke without anyone telling them. Nobody switches you off it automatically. You have to notice, and choose to leave.

How the Flat Rate Scheme is meant to work

The Flat Rate Scheme lets a VAT-registered business with taxable turnover up to £150,000 pay HMRC a fixed percentage of its VAT-inclusive turnover, instead of calculating output VAT on sales and separately reclaiming input VAT on purchases invoice by invoice. You still charge VAT to customers at the standard rate as normal, but what you hand over to HMRC is the flat percentage, not the exact output-minus-input figure. The trade-off is that you generally can't reclaim VAT on purchases separately, the flat rate is set with an assumed level of input VAT recovery already built in. General building or construction services sit at 9.5%; labour-only building or construction services sit higher, at 14.5%, reflecting how little a labour-only trade typically spends on VAT-bearing materials.

What the domestic reverse charge changed

Since 1 March 2021, most standard and reduced-rated construction services supplied between VAT and CIS-registered businesses fall under the domestic reverse charge, unless the customer is an end user or intermediary supplier who has confirmed that in writing. Under the reverse charge, the subcontractor doesn't charge output VAT on the invoice at all. The customer accounts for both sides of the VAT themselves. The subcontractor's invoice simply states that the reverse charge applies and specifies the VAT rate, with no VAT actually added to the amount charged.

That single change is what breaks the Flat Rate Scheme for most construction subcontractors. The scheme works by applying a percentage to VAT-inclusive turnover. A reverse-charged sale has no VAT on it to include. HMRC's own guidance is explicit: reverse charge sales are excluded from flat rate turnover entirely. You don't apply the flat rate percentage to them, and you don't add anything to your flat rate calculation because of them. They simply sit outside the scheme.

Why that leaves a subcontractor worse off, not just simpler

Picture a labour-only subcontractor whose customers are almost entirely VAT and CIS-registered main contractors. Under the reverse charge, the overwhelming majority of that turnover carries no VAT and is excluded from the flat rate calculation. What's left, the small proportion of sales to end users or non-registered customers where standard VAT still applies, is all the flat rate percentage now has to work with.

Meanwhile the other side of the bargain hasn't moved. The subcontractor still can't reclaim VAT on materials, small tools, fuel, or overheads under the Flat Rate Scheme, because that recovery is meant to be baked into the flat percentage they pay on turnover that, in practice, barely exists anymore. The scheme was priced assuming a mix of VATable sales against which input VAT recovery was implicitly netted off. Strip out most of the VATable sales and that pricing no longer holds. The subcontractor ends up paying VAT-bearing costs in full with nothing offsetting them, for the sake of a scheme that was supposed to save them administration, not money.

The limited cost trader rule makes it worse again

There's a second mechanism that compounds the problem for exactly this type of business. If your VAT-inclusive spending on goods is below 2% of turnover, or below £1,000 a year (pro-rated for shorter periods), HMRC classes you as a limited cost business and forces you onto a flat rate of 16.5%, regardless of your trade sector's normal rate. Labour-only subcontractors, the exact group also hit hardest by the reverse charge exclusion, are precisely the profile this test is designed to catch, since their spending is overwhelmingly on their own time rather than materials.

Put the two together and it's common to find a subcontractor stuck on the highest flat rate percentage available, applied to only a thin sliver of turnover that isn't reverse-charged, while every input VAT recovery opportunity on the rest of the business sits unused.

When staying on it can still make sense

The scheme isn't automatically wrong for every construction business. If most of your customers are private householders or non-VAT-registered clients, for example a small renovation or extension business working directly for homeowners, the reverse charge rarely applies and the Flat Rate Scheme can still function as intended. The issue is specifically for subcontractors whose customer base is dominated by other VAT and CIS-registered contractors, the exact relationships the reverse charge was built around.

Common mistakes

• Staying on the Flat Rate Scheme by default years after the reverse charge changed the customer mix, without ever re-running the numbers
• Not realising reverse-charged sales are excluded from flat rate turnover, and wrongly applying the percentage to them anyway
• Missing that limited cost business status can force the 16.5% rate regardless of trade sector, especially for labour-only subcontractors
• Assuming leaving the scheme means more admin than it actually does, when standard VAT accounting software handles most of the extra tracking automatically
• Not comparing actual input VAT recoverable under standard accounting against what the flat rate saving was actually worth before deciding either way

What actually protects you

Run the comparison properly rather than guessing: take a recent quarter, work out what standard VAT accounting would have produced with full input VAT recovery, and compare it to what the Flat Rate Scheme actually cost. For most subcontractors doing the bulk of their work for other CIS-registered contractors, the answer comes back the same way, standard accounting recovers more than the flat rate saves. Leaving the scheme is a straightforward notification to HMRC, and most bookkeeping software already handles standard VAT accounting without extra effort once you're set up on it.

Common questions

Can construction subcontractors still use the VAT Flat Rate Scheme?

Yes, joining is still technically allowed below the £150,000 turnover threshold, but the scheme has become far less useful since the domestic reverse charge for construction started. Reverse-charged sales are excluded from your flat rate turnover, so the percentage you pay HMRC only applies to whatever slice of income is not subject to the reverse charge, while you still cannot recover VAT on most purchases.

Why are reverse-charged sales excluded from Flat Rate Scheme turnover?

Under the domestic reverse charge, the subcontractor doesn't charge output VAT on the sale at all, the contractor accounts for it instead. Because the Flat Rate Scheme percentage is applied to VAT-inclusive turnover, a sale with no VAT charged on it produces nothing to apply the percentage to, so HMRC's guidance excludes reverse charge sales from the flat rate calculation entirely.

What is the limited cost trader rate and why does it hit construction subbies hardest?

If your VAT-inclusive spending on goods is below 2% of turnover, or below £1,000 a year, you're a limited cost business and must use a flat rate of 16.5% instead of your trade sector's rate, regardless of what that sector rate would otherwise be. Labour-only subcontractors who buy little beyond small tools and consumables are exactly the profile this test catches, on top of losing most of their turnover to the reverse charge exclusion.

Should a construction business leave the Flat Rate Scheme after the reverse charge?

For most subcontractors whose sales are mainly to VAT and CIS-registered contractors, yes. Standard VAT accounting lets you reclaim input VAT on materials, tools, fuel and overheads in full, which the Flat Rate Scheme does not allow outside certain capital purchases. Once the bulk of your turnover falls under the reverse charge, the Flat Rate Scheme is usually costing money rather than saving admin time.

This article is general information, not personal tax advice, and tax rules change. Your own position depends on facts we cannot see from here — please take advice before acting on anything above.

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