One of the most common questions we hear from growing businesses is: when do I need to register for VAT? It seems like it should be a straightforward answer — hit the threshold, register — but the mechanics of how that threshold works, and the deadlines that follow, catch a surprising number of business owners off guard.

The current VAT registration threshold is £90,000. But it’s not a fixed annual figure you check once a year. It’s a rolling 12-month test, and understanding that distinction is important. Miss the trigger point, and you could find yourself owing back-VAT on sales you’ve already received — plus a penalty on top.

In this post we’ll walk through when you’re legally required to register, what happens if you miss the deadline, the situations where you can apply for an exception, and whether registering early might actually work in your favour.

Most business owners understand there’s a VAT threshold. Where things get more complicated is understanding how it’s measured.

The £90,000 figure is based on your taxable turnover over any rolling 12-month period — not your financial year, not the tax year, and not a calendar year. HMRC expects you to check this at the end of every month. So if your turnover for the 12 months ending on 31 October exceeds £90,000, you’ve triggered the obligation, regardless of where that sits in relation to your accounts.

Taxable turnover for this purpose is broader than many people assume. It includes standard-rated, reduced-rated, and zero-rated sales. It also captures goods hired or loaned to customers, business goods used for personal purposes, and services subject to the reverse charge. What it doesn’t include is exempt income — so a business that earns exclusively from exempt supplies (certain financial services or medical care, for example) won’t be caught by the threshold in the same way.

The threshold has been £90,000 since 1 April 2024, when it rose from £85,000. The October 2026 Budget confirmed it will remain at £90,000 for now, so that’s the figure to plan against. There’s also a deregistration threshold of £88,000 — relevant if you’re already registered and your turnover drops.

There are two separate scenarios that require VAT registration, and the deadlines work differently for each.

You exceeded the threshold in the past 12 months

If your taxable turnover for the previous 12 months has gone over £90,000, you must notify HMRC within 30 days of the end of the month in which you crossed the threshold. Your effective date of registration is then the first day of the second month after you went over.

So if your rolling 12-month turnover crosses £90,000 on 15 October, you have until 30 November to register. Your VAT registration becomes effective from 1 December.

You expect to exceed the threshold in the next 30 days

If you have good reason to believe your taxable turnover will exceed £90,000 within the next 30 days — a large contract, a significant order — you must register by the end of that 30-day period. Crucially, your effective date of registration is the date you first realised you would exceed the threshold, not the date you actually cross it.

This second trigger is the one that tends to surprise people. If you sign a large contract on 1 November and it will push you over the threshold by month end, you should be registering immediately — not waiting to see whether the invoices go out in time.

Missing the registration deadline isn’t a minor administrative slip. The consequences are real, and they can be expensive.

If you register late, you’ll owe HMRC VAT on all sales made since the date you should have registered — not from the date you eventually got around to it. That means recalculating historical invoices, working out the VAT element, and paying it across. If your customers are VAT-registered themselves, you may be able to issue revised invoices and recover the VAT from them. If they’re consumers or unregistered businesses, that VAT comes out of your pocket.

On top of that, HMRC can charge a penalty of up to 30% of the VAT due where the failure wasn’t deliberate — and higher if it was. The penalty calculation considers how much you owe and how long you’ve been unregistered, so the longer you leave it, the worse it tends to get.

We see this more often than you’d expect — usually with businesses that have had a strong trading year and haven’t been monitoring their rolling turnover month by month. It’s entirely avoidable, but it requires the discipline of actually checking the numbers regularly, not just at year end.

If you think you may have missed the threshold date, the right move is to get advice promptly and approach HMRC proactively. Voluntary disclosure typically results in lower penalties than being caught.

There are a few situations that don’t follow the standard rules, and they’re worth knowing about.

Temporary spikes in turnover

If you’ve exceeded £90,000 in the past 12 months but can demonstrate that your turnover in the next 12 months is unlikely to exceed £88,000, you can apply to HMRC for an exception from registration. This is done via form VAT1 alongside a separate form VAT5EXC, which you request from HMRC directly. HMRC will consider the application and confirm in writing whether the exception is granted. It’s not automatic, and HMRC takes around 40 working days to respond — so it’s not a last-minute fix.

Non-UK businesses

If your business is based outside the UK but you’re making taxable supplies to the UK, the £90,000 threshold doesn’t apply to you. As a non-established taxable person (NETP), you must register as soon as you make any taxable supplies in the UK, regardless of their value.

Taking over a VAT-registered business

If you acquire an existing VAT-registered business, you’ll need to register if the combined taxable turnover of the acquired business and your existing business exceeds the threshold. This is an area where proper due diligence at the point of acquisition matters — it’s something we routinely check for clients going through a business purchase.

If your turnover is below £90,000, you don’t have to register — but you can choose to. And in certain situations, voluntary registration is genuinely worth considering.

The main benefit is the ability to reclaim VAT on your business costs. If you’re spending significant amounts on VATable purchases — equipment, software, professional services — you’re currently absorbing that VAT as a cost. Once registered, you can reclaim it. For businesses with high input costs relative to their sales, this can be a meaningful saving.

You can also backdate a voluntary registration by up to four years and reclaim VAT on eligible pre-registration costs, subject to the relevant conditions.

The trade-off is that once you’re registered, you must charge VAT on your sales. If your customers are mainly VAT-registered businesses, that’s usually fine — they reclaim it anyway, and your competitive position doesn’t change. If you sell predominantly to consumers or small unregistered businesses, adding 20% to your prices either reduces your margin or makes you less competitive.

We also find that voluntary registration makes sense for businesses that are growing toward the threshold anyway. Getting the systems and processes in place early — particularly with Making Tax Digital requirements in mind — is far less disruptive than scrambling to register at short notice when you’re already busy.