VAT registration is one of the most misunderstood milestones in a growing business, and getting it wrong is expensive. The threshold in 2026 is £90,000, but the part that catches people out is not the number, it is when you are actually required to register. Miss the deadline and HMRC can backdate your registration, leaving you to pay VAT out of your own pocket on sales where you never charged it.
This guide sets out the two tests that trigger registration, the exact deadlines, what counts towards the threshold, and the traps to avoid. Whether you are approaching £90,000 or just want to plan ahead, here is what you need to know.
In a nutshell
- Two separate tests can trigger registration. A backward look over 12 months and a forward look over 30 days.
- Taxable turnover is wider than you think. It includes zero-rated and reduced-rated sales.
- The deadline and start date differ by test. Getting the effective date right matters.
- Late registration can be very costly. HMRC backdates it and you owe the VAT anyway.
- You can register voluntarily below £90,000. Sometimes it pays, sometimes it does not.
- Registration changes how you operate. Digital records, returns and charging VAT.
1. The two tests that trigger registration
Most people know the £90,000 figure but not that there are two different ways to cross it. You must register if either applies.
The backward look test is the common one. If your total taxable turnover over the last rolling 12 months goes over £90,000, you must register. This is not your accounting year or the tax year, it is any rolling 12 month period, checked at the end of each month.
The forward look test is the one people miss. If at any point you expect your taxable turnover to go over £90,000 in the next 30 days alone, you must register immediately, even if your past turnover is tiny. This typically bites when you land a single large contract.
2. What counts as taxable turnover
The threshold is measured against taxable turnover, which is broader than many realise. It is the total value of everything you sell that is not VAT exempt or outside the scope of VAT.
Crucially, that includes zero-rated and reduced-rated sales, not just standard-rated ones. So a business selling mostly zero-rated goods can still be required to register even though it would charge little or no VAT. It also includes goods you hire or loan, business goods used personally, and certain reverse-charge services.
What it does not include is genuinely VAT-exempt income (such as some financial or insurance services) and anything out of scope. If most of your income is exempt, you may not need to register at all, but this is exactly the kind of judgement worth checking rather than guessing.
3. Deadlines and your effective registration date
The deadline and the date your registration actually starts depend on which test you triggered.
Under the backward look test, you must register within 30 days of the end of the month in which you went over £90,000. Your effective date of registration is the first day of the second month after you crossed the threshold. For example, if you went over on 15 July, you must register by 30 August, and you are VAT registered from 1 September.
Under the forward look test, you must register by the end of the 30 day period, and your effective date is the date you realised you would go over, not the date you actually did. So if on 1 May you sign a contract that will take you over within 30 days, you are registered from 1 May.
Getting this date right matters, because you must charge VAT from your effective date, whether or not your registration number has arrived yet.
4. The backdating trap and late penalties
This is where late registration becomes painful. If you register late, HMRC backdates your registration to the date you should have registered. From that date you are liable for the VAT on all your taxable sales, even though you never charged it to your customers. Going back to ask customers to pay VAT months later is awkward at best and often impossible, so it frequently comes out of your own margin.
On top of the VAT itself, HMRC charges interest from the date the VAT was originally due, and can add a failure to notify penalty. That penalty is based on the VAT you should have paid and on your behaviour. For a non-deliberate failure it can be up to 30% of the VAT due, but it can be reduced significantly, potentially to nothing, if you come forward voluntarily and promptly rather than waiting for HMRC to find you. A genuine reasonable excuse can remove the penalty altogether.
The lesson is simple: watch your rolling turnover monthly, and act the moment you are close, not after you have sailed past.
5. Should you register voluntarily
You can choose to register for VAT even if your turnover is below £90,000, and for some businesses it is a smart move.
The main benefit is that you can reclaim the VAT on your business purchases and expenses. If you sell mainly to other VAT-registered businesses, or you have significant costs with VAT on them, voluntary registration can genuinely save you money. It can also lend credibility, since a VAT number can make a small business look more established.
The downside is that you must add 20% VAT to your prices. If your customers are mostly members of the public or small non-registered businesses who cannot reclaim it, that makes you either more expensive or less profitable. Voluntary registration also brings the full compliance burden of returns and digital record keeping. It is a genuine cost-benefit decision, not an automatic yes.
6. What changes once you are registered
Once registered, VAT becomes a regular part of running your business. You must charge VAT on your taxable sales at the right rate, usually 20%, and show it correctly on your invoices.
You will also file VAT returns, normally every quarter, and pay any VAT due to HMRC. Every VAT-registered business must now keep digital records and file through Making Tax Digital compatible software, so a spreadsheet and a shoebox of receipts no longer meets the rules. In return, you reclaim the VAT on your eligible business costs, which offsets what you owe.
None of this is difficult with the right setup, but it does need to be in place from your effective date, not whenever you get around to it.
A worked example: Daniel, a growing builder
Daniel runs a building firm and watches his turnover creep up. By the end of June his rolling 12 month taxable turnover reaches £92,000, so the backward look test is triggered. He must register by 30 July, and his effective date is 1 August. From 1 August he charges VAT on his work.
Now imagine instead that in May Daniel signs a single £100,000 contract due to start and complete within 30 days. That triggers the forward look test on the day he signs. He must register within 30 days, and his effective date is that signing date, so VAT applies to that contract from the start.
If Daniel had ignored either trigger and registered six months late, HMRC would backdate him, and he would owe roughly £15,000 to £18,000 of VAT on work where he never charged it, plus interest and a possible penalty. Registering on time costs nothing extra.
Things to watch out for
- Check your rolling 12 months monthly. The test is not your financial year, it is any 12 month window.
- A single big contract can trigger it instantly. The forward look test does not wait for past turnover.
- Zero-rated sales still count. They go towards the £90,000 even if you charge no VAT.
- You can deregister below £88,000. If your taxable turnover falls under the deregistration threshold, you may be able to come out.
- Charge VAT from your effective date. Even before your number arrives, adjust your pricing so you are not caught short.
How Ollen Services Can Help
VAT registration is easy to get wrong and expensive to fix after the fact. We monitor your turnover against both tests, tell you exactly when and how to register, and make sure you never stumble into a backdated registration and an out of pocket VAT bill.
If you are weighing up voluntary registration, we will run the numbers for your specific customer base and cost profile so you make the decision that actually benefits you, then set up your digital records and returns so compliance is painless from day one.
Call us on 07513 491 259 or email hello@ollenservices.co.uk. If you are anywhere near £90,000, a quick review now can save you thousands later.