Does the £90,000 threshold apply to my profit or my sales?

Sales, not profit, and that catches people out badly. The test is your VAT-taxable turnover: the total value of everything you sell that is not exempt or outside the scope of VAT, before you deduct a single cost. A trades business turning over £110,000 with £70,000 of materials and subcontractors has taxable turnover of £110,000, not £40,000 of profit. It is over the threshold and must register. The only things you strip out are genuinely exempt income, such as some financial services or certain rents, and anything outside the scope of UK VAT. Everything else — standard-rated, reduced-rated and zero-rated alike — counts towards the £90,000.

I went over the threshold months ago and did nothing. What happens now?

Register straight away and tell HMRC before they tell you. HMRC backdates your registration to the date you should have been registered, and you owe VAT on every sale made since, even though you never charged your customers a penny of it. On top sits a failure to notify penalty, calculated as a percentage of the tax owed. Where the failure was non-deliberate and you come forward unprompted within twelve months of the tax becoming due, the range runs from 0% to 30%, so a full and early disclosure can genuinely land at nothing. Wait until HMRC prompts you more than twelve months on and the range starts at 20%.

Can I charge VAT before my registration number arrives?

You cannot show VAT on an invoice until you have your number, but you are liable for it from your effective date of registration regardless. The usual fix is to raise invoices for the VAT-inclusive amount without showing VAT separately, tell the customer a full VAT invoice will follow, then reissue proper VAT invoices once the number lands. That way you have actually collected the money you will owe HMRC. The alternative, invoicing at your old net prices and hoping to go back to customers weeks later, is exactly how businesses end up paying a sixth of several weeks of sales out of their own margin.

Does one big contract on its own force me to register?

Yes, if you expect it to take your VAT-taxable turnover over £90,000 within the next 30 days on its own. This is the forward-look test and it runs separately from the rolling twelve-month one. It bites on the day you become aware, not the day the money arrives or the job completes. So a builder who signs a £95,000 fit-out on 4 September, expecting to invoice it within the month, must register from 4 September, even if last year's turnover was £40,000. Price the job VAT-inclusive from the outset. Discovering afterwards that a fifth of the contract value belongs to HMRC is a painful way to learn the rule.

Should I register voluntarily if I sell to the public?

Usually not. Members of the public cannot reclaim VAT, so registering leaves you two poor options: raise prices by 20% and become less competitive, or hold prices and hand a sixth of every sale to HMRC out of your own margin. On £60,000 of sales that is £10,000 of margin gone, offset only by whatever input VAT you can reclaim on costs. It can still make sense where you buy a lot of standard-rated stock or equipment, because the reclaim outweighs the loss. Do the sums both ways on your own numbers first. Registering is quick; getting back out means waiting until turnover falls below £88,000.

All my sales are zero-rated. Do I still have to register?

Yes. Zero-rated is not the same as exempt, and the distinction costs people money. Zero-rated sales are taxable supplies that happen to carry a rate of 0%, so they count in full towards the £90,000 rolling total. Cross it and you must register, even though you will charge your customers nothing. The upside is real: registration lets you reclaim input VAT on your costs while collecting none on your sales, which usually produces a repayment rather than a bill. You can apply for exemption from registration where your supplies are wholly or mainly zero-rated, but for most businesses in that position registering is the more profitable answer.

When Do I Need to Register for VAT?

Here is the short answer: you must register for VAT once your VAT-taxable turnover goes over £90,000. That threshold has applied since 1 April 2024 and it is unchanged for the 2026/27 tax year. The deregistration threshold sits just below it, at £88,000.

One sentence, though, hides the details that trip people up constantly. The threshold is not measured over the period most people assume, there is a second test that works in the opposite direction, and the penalty for missing both falls on you rather than your customers. Here is how it actually works.

The £90,000 threshold is a rolling 12-month test

This is the single biggest misunderstanding we see. The threshold is not based on your tax year, your accounting year, or the calendar year. It works on a rolling 12-month basis.

At the end of every single month, you look back over the previous 12 months and add up your VAT-taxable turnover. If that running total has gone over £90,000, you have crossed the threshold — even if your official accounting year has barely started.

So a business invoicing £8,000 in a good month, month after month, will quietly sail past £90,000 partway through the year. The trap is that people only look at turnover once a year at accounts time, by which point they may have been trading over the threshold for months without knowing it.

Several things count towards VAT-taxable turnover that people forget:

Standard-rated, reduced-rated and zero-rated sales all count. Zero-rated is still a taxable supply — it simply carries a rate of 0%.
Sales to customers who are themselves VAT registered count in full.
Genuinely VAT-exempt income, such as some financial services or certain rents, does not count, and neither does anything outside the scope of UK VAT.
It is turnover, not profit. Your costs come nowhere into it.

The 30-day forward-looking test

There is a second, separate test running alongside the rolling one, and it looks forwards.

If at any point you expect your VAT-taxable turnover to go over £90,000 in the next 30 days alone, you must register immediately — and registration takes effect from the date you realised, not from the end of the 30 days.

This one bites when a big contract lands. If you win a single order that will, on its own, take you over the threshold within a month, you cannot wait for the rolling total to catch up. The classic case is a tradesperson signing a large fit-out: the moment they know that job will breach £90,000 inside 30 days, they are on the hook.

What are the deadlines?

Under the rolling test, you must register within 30 days of the end of the month in which you went over. Your registration then takes effect from the first day of the second month after you went over.
Under the 30-day forward test, you must register by the end of that 30-day period, and you are registered from the date you first expected the breach.

Miss these and HMRC registers you retrospectively anyway — which leads to the most expensive mistake in this guide.

What late registration actually costs: a worked example

Illustrative figures throughout — not a client, just arithmetic you can follow with your own numbers. A one-van landscaping business invoices between £7,000 and £9,000 a month, all to homeowners. Its rolling 12-month total passes £90,000 at the end of August 2026.

The rolling test says register within 30 days of that month end — by 30 September 2026.
Its effective date of registration is the first day of the second month after it went over: 1 October 2026.

The owner never checks, and carries on as normal. In March 2027 the accounts are prepared and the breach comes to light. By then the business has invoiced £48,000 across the six months from October to March, with no VAT charged on any of it.

That £48,000 is now treated as VAT-inclusive. The VAT inside it is £48,000 × 1/6 = £8,000, and it is owed to HMRC. The customers were households. None of them is going to pay it now. So the full £8,000 comes off the owner's own margin.

Then the penalty. Failure to notify is charged as a percentage of that £8,000, and the range depends entirely on how HMRC finds out:

Non-deliberate, disclosed unprompted within 12 months of the tax becoming due: 0% to 30%. A good disclosure can genuinely land at nothing.
Non-deliberate, prompted by HMRC more than 12 months on: 20% to 30% — on £8,000, a further £1,600 to £2,400.
Deliberate: 20% to 70% unprompted, 35% to 70% prompted.
Deliberate and concealed: 30% to 100% unprompted, 50% to 100% prompted.

Registering on time was free. Not noticing cost £8,000 before a penny of penalty or interest. That is the entire argument for the five-minute monthly check at the end of this guide.

Voluntary registration: when it helps, when it hurts

You are allowed to register before you hit £90,000. Sometimes that is genuinely smart; sometimes it just adds admin for no gain. The deciding factor is almost never your turnover. It is who your customers are.

It can help when:

Most of your customers are VAT registered themselves. They reclaim the VAT you charge, so your effective price to them does not move — and you get to reclaim VAT on your own costs.
You buy a lot of standard-rated stock, equipment or services, so input VAT reclaims put real money back.
A VAT number makes you look established to the customers and suppliers you want to win.

It can hurt when:

Your customers are mainly the public or small unregistered businesses. They cannot reclaim, so you either become 20% dearer or absorb a sixth of every sale.
You have few costs carrying VAT, so there is little to reclaim.
You do not want the quarterly filing obligation yet.

Putting numbers on the voluntary decision

Two illustrative businesses, identical turnover, opposite answers. Both do £70,000 a year with £14,000 of standard-rated costs.

Business A sells to VAT-registered companies. It registers voluntarily and adds 20% to its invoices. Its customers reclaim every penny, so the real price to them is unchanged. It reclaims the input VAT on its costs: £14,000 × 1/6 = £2,333. Net effect: roughly £2,333 a year better off.

Business B sells to households. Same figures. If it holds its prices, the £70,000 becomes VAT-inclusive and £70,000 × 1/6 = £11,667 goes to HMRC. Reclaiming the same £2,333 leaves it £9,334 a year worse off. If instead it raises prices by 20%, it protects the margin but is now the dearest quote on every job.

Same turnover, same costs, an £11,667 swing — decided entirely by who is on the other side of the invoice. Run your own version before you volunteer for it, and our VAT calculator will do the arithmetic.

What registration actually means day to day

Once registered, three things change:

You must charge VAT on your standard and reduced-rated sales, show it on your invoices, and hand it to HMRC. It was never really yours — you are collecting on their behalf.
You can reclaim VAT on most business purchases.
You must file VAT returns, usually quarterly, and pay any difference across.

Returns must be kept and filed digitally under Making Tax Digital: records in compatible software, submitted straight from it, with no typing figures into a web form. Our guide to Making Tax Digital and the MTD service page cover how that works. Get your bookkeeping onto proper software before you register, not after.

The Flat Rate Scheme, and the trap inside it

If your turnover is modest, the Flat Rate Scheme simplifies things. Instead of calculating VAT on every sale and purchase, you pay HMRC a fixed percentage of your VAT-inclusive turnover, set by your trade sector. You still charge customers the normal 20% and keep the difference.

The rules worth knowing:

You can join if your VAT turnover is £150,000 or less, excluding VAT.
You must leave when your total VAT-inclusive income reaches £230,000 in the year to your anniversary date — or immediately if you expect to pass £230,000 in the next 30 days alone. HMRC may let you stay if it is satisfied your turnover for the coming year will fall below £191,500.
You get a 1% reduction in your flat rate for the first 12 months after VAT registration.
If you are a limited cost business, your rate is 16.5% whatever your sector. That applies where your spending on relevant goods is under 2% of your flat rate turnover, or over 2% but less than £1,000 a year (£250 a quarter).

That last bullet is the trap, and it catches consultants, contractors and anyone whose costs are mainly their own time. Illustrative arithmetic: a consultant with £80,000 of VAT-inclusive turnover and £6,000 of VAT-bearing costs. As a limited cost business they pay 16.5% × £80,000 = £13,200, while charging customers £80,000 × 1/6 = £13,333 — a gain of £133, with no input VAT reclaim at all. On the standard scheme they would pay over £13,333 and reclaim £1,000 on those costs, a net £12,333. The Flat Rate Scheme leaves them £867 a year worse off. Do the sums both ways before you opt in.

The penalties once you are registered

Registering is only half of it. Two separate penalty regimes then apply.

Late returns work on points. Each late submission earns a penalty point. Hit the threshold for your filing frequency and you get a £200 penalty, plus another £200 for every further late return while you remain at the threshold. The thresholds are 2 points for annual filers, 4 for quarterly, 5 for monthly — so a quarterly filer has a full year of slippage before the first fine, and then they come one after another.

Late payment is charged in two stages, at rates increased from 1 April 2025. The first penalty is 3% of what is still outstanding at day 15, plus a further 3% of what is outstanding at day 30. From day 31 a second penalty accrues daily at an annual rate of 10%, and late payment interest runs on top.

Put figures on it. £10,000 of VAT paid 40 days late costs 3% at day 15 (£300), 3% at day 30 (£300), and roughly £27 of second penalty for the ten days past day 31 — about £627, plus interest. Paid on day 14, it costs nothing. Our post on the real cost of late VAT returns goes further into this.

Common traps to avoid

Leaving registration too late. HMRC backdates it, you owe VAT on sales where you charged none, and the money comes out of your own pocket. This is the big one.
Only checking turnover once a year. The test is rolling. It needs looking at every month.
Forgetting zero-rated sales count. They push you towards £90,000 like any other taxable supply.
Assuming a quiet month resets the clock. It does not. The window always looks back a full 12 months.
Confusing turnover with profit. A business with £110,000 of sales and £70,000 of materials is over the threshold, not £40,000 under it.
Splitting a business to stay under. HMRC can issue a direction treating artificially separated businesses as one for VAT. Structure for commercial reasons, not to dodge the threshold.

Deregistration

VAT is not necessarily forever. You can ask HMRC to cancel your registration if your VAT-taxable turnover falls below £88,000 and you expect it to stay there. You must cancel, within 30 days, if you stop trading or stop making taxable supplies, or if you join a VAT group. Deregistering means one final return and, sometimes, accounting for VAT on stock and assets you still hold — so it is worth planning rather than rushing.

The five-minute check to do this week

This is the whole guide reduced to something you can actually action:

Open your accounting software and run a sales report for the last 12 complete months.
Strip out genuinely exempt and out-of-scope income. Leave zero-rated income in.
Compare the total with £90,000.
If you are within £10,000 of it, put a recurring reminder in your diary for the last working day of every month and repeat steps 1 to 3.
If you have signed, or are about to sign, anything that would add £90,000 of taxable sales inside 30 days, register now rather than at the end of the job.

Five minutes a month. Against an £8,000 mistake, it is the best-value task in your calendar.

The honest summary

Register when the rolling 12-month total tips over £90,000, or the moment you know you will breach it in the next 30 days — whichever comes first. Consider registering voluntarily if you sell mainly to other VAT-registered businesses, and almost certainly not if you sell to the public. Watch the rolling total monthly, because the costliest mistake in VAT is finding out you crossed the line six months ago.

If you are not sure where your running total sits, or whether voluntary registration would help or hurt in your case, it is a five-minute conversation rather than a guessing game. Our blog post on when to register for VAT covers the same ground from a different angle, and you can get in touch here and we will check the figure with you before it becomes a problem.