VAT mistakes are rarely about “not knowing VAT”. More often, they come from day-to-day pressures – rushed bookkeeping, inconsistent coding, a new income stream or a well-meaning change to pricing that was not tested for VAT. The problem is that VAT errors tend to snowball. A small treatment issue can repeat across every invoice, every quarter and every return, turning into a material liability and a cashflow shock.

HMRC’s own data shows why it pays to stay on top of this. The first estimate of the VAT gap for 2024 to 2025 is 6.2%, equivalent to £11.4bn. That gap includes error, failure to take reasonable care and evasion – and it drives compliance activity. See HMRC’s preliminary estimate of the VAT gap (tax year 2024 to 2025).

Below, we cover VAT mistakes we commonly see around partial exemption, flat rate scheme (FRS) percentages, fuel scale charges and VAT on digital services. We also include a practical self-check flow, plus when and how to disclose errors.

If you want support, start with our VAT services – we can help you identify issues early and keep your VAT position defensible.

Why VAT mistakes are showing up more often

Three things tend to bring VAT mistakes to the surface.

More data and better matching: With Making Tax Digital for VAT and wider use of digital bookkeeping, VAT returns often align more closely to sales and purchase ledgers. That makes patterns easier to spot.
Business models shifting: Subscriptions, mixed taxable and exempt income, cross-border customers and bundled services all increase the risk of misclassification.
Cash pressure decisions: Businesses sometimes change pricing, invoicing or supplier choices quickly to protect cashflow. VAT treatment can be missed in the process.

The aim is not to eliminate every judgment call. It is to reduce repeatable VAT mistakes, document the reasoning and correct errors promptly when you find them.

Partial exemption: The VAT mistake that creeps in quietly

Partial exemption problems tend to affect businesses with a mix of taxable and exempt supplies. It is common in sectors like property, financial services, education and healthcare-adjacent work, but it can also appear in “ordinary” small and medium-sized enterprises (SMEs) – for example, where you have a taxable trading business alongside exempt income such as rent.

Common VAT mistakes we see include the following.

Misclassifying income streams: Treating exempt income as outside the calculation or treating zero-rated supplies as exempt. Zero-rated is taxable, exempt is not.
Using a method that no longer reflects the business: The standard method is often used by default. Over time, it can produce unfair results if your cost base or income mix changes.
Forgetting annual adjustments: A quarterly calculation is not the end of it. Many partial exemption methods require an annual adjustment and missed adjustments can accumulate.
Ignoring de minimis checks: Some businesses assume they are “partly exempt so we cannot reclaim much VAT”, when the de minimis test would allow full recovery for a period.

Example: You run a consultancy that mostly provides standard-rated services, but you also earn exempt commission income. You reclaim input VAT in full because “the trading side is the real business”. Later, commission becomes a larger share, and your recoverable input VAT should reduce. If nothing changes in your VAT workings, the VAT mistake repeats every quarter.

Practical fix: Build a quarterly prompt into your VAT review. Ask, “Have we added any exempt income, property income, finance income or commission streams this quarter?” If yes, test the partial exemption position before filing.

Flat rate scheme percentage errors, and the limited cost business trap

The FRS can simplify VAT, but only if the basics are right. Many VAT mistakes come from choosing the wrong sector percentage or failing to apply the limited cost business rules.

What tends to go wrong

Wrong trade sector: Some businesses pick a sector that sounds close rather than the one that best matches what you actually supply. If the percentage is too low, the underpayment can be significant.
Not reassessing after a change in activity: The sector choice is not “set and forget”. If your income mix changes, your percentage might need to change too.
Limited cost business not identified: If your goods spend is low, HMRC may treat you as a limited cost business, which pushes you onto a higher flat rate percentage. We often see this missed where costs are mainly labour, software subscriptions or subcontractors.
Turnover errors: FRS is calculated on VAT-inclusive turnover. Misposted sales, credit notes or mixed VAT liability supplies can distort the figure.

Example: A service business uses the FRS to simplify reporting. Over time it moves to remote delivery, outsources more and buys fewer goods. It may fall into the limited cost business category. If the higher percentage is not applied, a VAT mistake builds each quarter.

Practical fix: Check your goods spend each quarter and document it. If your business model is service-heavy, do not assume the original FRS percentage still applies.

Fuel scale charges: A small missed step with a predictable HMRC view

Fuel scale charges are designed to deal with private use of fuel in business vehicles where you reclaim input VAT on road fuel. If you reclaim VAT on fuel and there is any private use, HMRC expects a fuel scale charge (unless you can demonstrate there is no private use, which is often hard in practice).

Common VAT mistakes we see

Reclaiming VAT on fuel without applying the scale charge: This is the classic issue. It usually appears when bookkeeping is done quickly and VAT is reclaimed on all fuel invoices as a matter of routine.
Applying the wrong scale charge band: The charge depends on the vehicle’s CO₂ emissions. Using an old banding or an estimate can create errors.
Inconsistent treatment across vehicles: One vehicle is treated correctly, another is not, often because the CO₂ data is not held centrally.

HMRC publishes the current rates here: VAT road fuel scale charges from 1 May 2025 to 30 April 2026.

Practical fix: Decide on a policy per vehicle and stick to it. Either:

reclaim VAT on fuel and apply the scale charge correctly, or
restrict input VAT claims where appropriate, supported by records.

VAT on digital services: The “place of supply” VAT mistake

Digital services can create VAT mistakes because the VAT treatment depends on who the customer is (business or consumer), where they belong and what you are actually supplying.

Typical problem areas

B2C sales outside the UK: If you sell digital services to consumers outside the UK, local VAT rules may apply. For the EU in particular, the customer’s location and the nature of the service matter.
B2B cross-border services: The reverse charge can apply in many B2B cases, but you need the right evidence and invoicing wording.
Marketplaces and app stores: If a platform is the “deemed supplier”, your VAT obligations may change. Businesses sometimes account for VAT twice, or not at all, because they have not confirmed who is supplying the service.
Bundled services: If you sell a subscription that includes access, support and optional add-ons, VAT liability can depend on whether it is a single supply or multiple supplies.

Practical fix: For any new digital income stream, stop and run a short VAT treatment review before you start invoicing at scale. The right answer early is usually far cheaper than fixing VAT mistakes later.

A VAT mistakes self-check flow you can run before every return

Use this as a repeatable process. It is designed to catch VAT mistakes before submission, without turning your VAT return into a major project.

Confirm what changed this period: new products, services, pricing models, customer locations or major suppliers.
Review the exceptions list: unusual invoices, credits, zero-rated sales, exempt income and large purchases.
Test partial exemption triggers: any exempt supplies, property income, commission or finance income.
Check scheme consistency: if you are on FRS, confirm the sector percentage still fits and reassess limited cost status.
Validate fuel treatment: if you reclaimed VAT on road fuel, confirm whether a fuel scale charge is required and applied.
Sense-check digital services: B2C or cross-border sales, platform sales and evidence for customer status.
Run a “top 10” VAT code review: scan the 10 largest input VAT and output VAT entries for the quarter.
Document your judgment calls: keep brief notes and supporting evidence for anything not straightforward.

If you want a second pair of eyes, we can build this into a VAT health check as part of our VAT services.

When you should disclose VAT mistakes, and how to do it

Not every error requires a separate disclosure to HMRC, but you need to follow the correct route.

HMRC’s guidance explains when you can adjust errors in a subsequent VAT return and when you must report them separately. It also reflects the withdrawal of VAT652 and the current reporting process. See VAT Notice 700/45: how to correct VAT errors and make adjustments or claims.

As a practical rule of thumb, consider the following.

Size and nature of the error: Larger errors and deliberate or careless issues are more likely to need direct reporting.
Timing: The longer an error runs, the more HMRC may expect you to address it formally, not just “fix it going forward”.
Behaviour and evidence: Penalties often depend on whether you took reasonable care and how you responded when the issue was identified. A prompt, well-evidenced disclosure generally puts you in a better position.

If you are concerned the error could lead to a compliance check or dispute, it can be sensible to get advice early. Where HMRC inquiries are already underway, our tax investigation support can help you manage the process and responses in a controlled way.

Fixing VAT mistakes before they become expensive

VAT mistakes are usually fixable, but the cost of fixing them depends on how early you act and how well you can evidence your position. The aim is to reduce repeat errors, keep your VAT treatment consistent with what you actually do, and correct problems in the right way when they show up.

If you take one thing from this, make it this: run a short pre-filing review every quarter, and treat changes in income streams, schemes and vehicle use as VAT triggers. That approach protects your cashflow, reduces the risk of penalties and helps you avoid the stress of a surprise HMRC letter.

If you would like us to review your position, we can run a focused VAT health check that targets the areas where VAT mistakes most often occur – partial exemption, FRS percentage selection, fuel scale charges and digital services treatment. To discuss a VAT health check and reduce VAT mistakes before HMRC contacts you, please get in touch with us.

VAT mistakes we keep seeing – and how to fix them before HMRC calls