What happens if I go over the VAT threshold by accident or temporarily?

Two very different situations, often confused

The question "what happens if I went over the threshold" actually covers two distinct scenarios that need different responses:

• By accident: you've crossed £90,000 some time ago without noticing, and you're only realising now. The clock has been running and you may already be in late-registration territory.
• Temporarily: a one-off event (a single large contract, a seasonal spike, an exceptional project) has pushed you over £90,000 in the rolling 12 months, but you're confident you'll fall back below before long.

The two situations have different paths through HMRC, different forms, different risks, and different costs. The accidental path leads to unprompted disclosures and penalty mitigation. The temporary path leads to the exception from registration, covered in detail below. Confusing them costs money.

If the breach is genuinely temporary: the exception from registration

HMRC recognises that some businesses cross the £90,000 line because of one-off events rather than sustained growth. In those cases, you can apply for an exception from registration. If granted, you stay outside the VAT system despite the rolling figure showing a breach.

The legal test is simple in principle: you have to satisfy HMRC that your taxable turnover in the next 12 months will not exceed the deregistration threshold of £88,000. Notice two things:

• The forward projection is 12 months from the trigger, not from the application date
• The figure is £88,000, not £90,000. The £2,000 buffer matters and is often misread

What HMRC actually requires

The exception isn't a tick-box approval. HMRC reviews the case on its merits, and the burden of proof is on the business. The application typically needs to include:

• Form VAT1 (the standard registration form, completed in full)
• Form VAT5EXC (the exception-specific form, requesting the exemption from registration)
• Supporting evidence of why the breach was temporary and why turnover is not expected to exceed £88,000 in the next 12 months

The evidence is where most applications succeed or fail. HMRC looks for:

• Copies of the one-off contract or event that caused the breach, including start and end dates
• Detailed sales forecasts for the next 12 months showing the expected decline back below £88,000
• Historical turnover data showing a consistent pattern well below the threshold prior to the spike
• Correspondence or documentation confirming that a specific project has concluded and will not be renewed
• Any contextual evidence that supports the case (industry conditions, customer behaviour, business model)

"I just think it was a one-off" isn't evidence. Detailed numerical forecasts based on documented business reality are.

Where this gets ambiguous: the line between "one-off event" and "growth that may continue" is exactly where exception applications get refused. A business with a clearly time-bounded contract that's now ended has a strong case. A business that "had a busy quarter" or "an unusually good run of clients" has a much weaker one. The same numerical breach can be granted an exception in one case and refused in another, depending entirely on the evidence narrative.

How HMRC responds and what happens next

HMRC will typically respond to an exception application within 40 working days. There are three possible outcomes:

The exception is granted

You stay outside the VAT system. You must continue to monitor your turnover monthly, and the obligation to notify HMRC reapplies if you cross the threshold again. The exception covers the specific 12-month projection submitted, not a permanent waiver.

The exception is refused

Registration goes ahead based on the original trigger date. From your effective registration date (typically the first day of the second month after you crossed the threshold), you owe VAT on all taxable sales, even if you didn't charge it at the time. That backdated VAT comes out of your margin.

If your notification was late or absent, you may also face a failure-to-notify penalty on top of the backdated VAT. The penalty is reduced for unprompted disclosures and increased for deliberate or careless failures.

HMRC asks for more information

In some cases, HMRC will request additional evidence before deciding. The 40-day clock can reset or extend in these situations. Cooperating fully and quickly tends to produce better outcomes than treating the queries as a delay tactic.

If the breach was accidental: the unprompted disclosure path

If you've discovered you crossed the threshold months or years ago without registering, the right path is usually different. Rather than an exception application, you typically need to make an unprompted disclosure to HMRC, registering retrospectively from the correct effective date.

The reason this path matters: HMRC's penalty regime distinguishes sharply between unprompted disclosures (where you come forward voluntarily) and prompted disclosures (where HMRC has contacted you or you only acted because you knew they were about to). The financial difference can be substantial.

An unprompted disclosure typically involves:

• Identifying the correct effective registration date based on when the threshold was crossed
• Calculating backdated VAT on all taxable sales since that date
• Working out whether to attempt customer reimbursement (often impractical) or absorb the VAT
• Submitting the late registration with a clear explanation of how the breach occurred and was discovered
• Negotiating penalty mitigation based on the unprompted nature and any reasonable excuse arguments

This is procedural ground where preparation before contacting HMRC tends to pay off. The first letter from you typically anchors the conversation, and getting the calculation, narrative, and tone right at that stage influences the outcome.

The four scenarios we see most often

In practice, businesses who arrive at this question fall into one of four situations, each with a different best response:

One-off contract just ended

You took on a single project that pushed your taxable turnover above £90,000, the project has now ended, and your underlying trading pattern is comfortably below the threshold. This is the textbook case for an exception application. The evidence is straightforward, the projection is credible, and HMRC is most likely to grant the exception.

Busy season just finished

A seasonal business (tourism, retail with strong peaks, summer-only operations) crossed the threshold during a peak month and is now back in low season. The "temporary" framing is intuitive but harder to evidence, because seasonal peaks tend to recur. HMRC will want to see why next year's peak won't trigger the same outcome.

Growth that may or may not continue

You crossed the threshold during a phase of expansion and you're genuinely unsure whether this is a permanent move up or a temporary blip. This is the hardest case for an exception. HMRC's default position will be that growth continues unless you can show otherwise, and "I'm not sure" tends to be read as "registration applies".

Late discovery

You're realising for the first time that the threshold was crossed weeks or months ago. The exception path is rarely the right one here, even if the breach was originally temporary, because the notification deadline has already passed. The unprompted disclosure route generally applies, with penalty mitigation discussions as a separate workstream.

What to do, in order

1. Establish the actual position. Calculate your rolling 12-month taxable turnover precisely, identify the exact month the breach occurred, and confirm whether the trigger is the historical test, the forward-look test, or both
2. Identify which situation you're in: genuinely temporary (with the evidence to back it), accidental late discovery, or something in between
3. Notify HMRC within the 30-day deadline if you're still inside it. The notification is required regardless of whether you intend to apply for an exception
4. If applying for an exception: prepare VAT1, VAT5EXC, and the supporting evidence package. Submit as a coherent application, not in stages
5. If pursuing unprompted disclosure: calculate the backdated VAT position, prepare the disclosure narrative, and contact HMRC before they contact you
6. Continue monitoring monthly, regardless of which route you're on. The obligation doesn't pause while HMRC reviews

The situations that most often turn into costly mistakes

Temporary or accidental breaches are exactly where the gap between what businesses think happens and what actually happens is widest. The situations below are where the cost most often materialises, sometimes months after the original breach:

• You've crossed £90,000 because of a specific contract or event and want to know whether an exception application is realistic in your case
• You're a seasonal business and want to understand how the exception rules apply where peaks recur year after year
• You've discovered the threshold was crossed some time ago and need to handle the disclosure to HMRC properly, before they discover it themselves
• You applied for an exception and it was refused, and want to understand whether to appeal or simply register
• You were granted an exception but your circumstances have shifted, and you want to know whether the original protection still applies
• You're not sure which path applies (temporary breach vs late discovery), and want a clear-eyed view before contacting HMRC
• HMRC has written to you about a suspected late registration and you need to respond properly

Whether you're a business owner or an accountant working on a client case, we focus on the VAT questions where extra expertise pays off, and we work in plain English.