Somewhere around £85,000 of turnover something perverse happens to a growing sole trader. The reward for a good year is either a 20% price rise your customers have to absorb, or a sixth of your revenue handed to HMRC. That is the VAT cliff, and it is the sharpest edge in the UK tax system for a one-person business.
It is also the edge people walk off without noticing, because the test is not the one they assume. Below is exactly how the threshold works, what crossing it costs in pounds, and the four decisions that separate a planned step up from an expensive surprise.
The test is rolling, and that is why people miss it
You must register for VAT once your total taxable turnover for the last 12 months goes over £90,000. That figure has been £90,000 since 1 April 2024. Two features of it catch people out.
The first is that the twelve months is rolling. It is not your tax year and not the calendar year. On 31 August you test the twelve months to 31 August. On 30 September you test the twelve months to 30 September, which drops last September off the back and adds this September on the front. The window moves every single month, so a strong autumn followed by one large January job can push the trailing twelve over the line in February — nowhere near any date you had in the diary.
The second is that it is turnover, not profit. Standard-rated, reduced-rated and zero-rated sales all count towards it. Your costs are irrelevant to the test. A trade running £30,000 of materials through the books reaches £90,000 of turnover far sooner than the owner's income would suggest.
There is also a second test that works forwards rather than backwards. If at any point you realise your taxable turnover will exceed £90,000 in the next 30 days alone — one contract, one order — you must register immediately, without waiting for the rolling total to catch up.
The two dates that follow, and they are not the same date
Once the rolling total crosses, you have 30 days from the end of the month in which you went over to register. Your effective date of registration is then the first day of the second month after you went over. Those are two different dates and the gap between them is where the money is.
• The month he went over is May, so his registration deadline is 30 June 2026.
• His effective date of registration is 1 July 2026 — the first day of the second month after May.
• Every invoice he raises from 1 July must carry VAT, whether or not his registration number has arrived yet.
That last point is the one that stings. HMRC can take several weeks to issue a number, and you cannot show VAT on an invoice without one. The standard fix is to raise invoices for the VAT-inclusive amount without showing VAT separately, then reissue proper VAT invoices once the number lands. If you simply invoice as though nothing changed, the VAT still becomes due — out of your own margin.
Under the forward-look test the effective date is different again: it is the date you realised you would cross, not the start of a later month.
What crossing costs when you sell to consumers
If your customers are VAT-registered businesses, crossing barely registers. They reclaim what you charge, so your price to them is unchanged in real terms, and you start reclaiming VAT on your own costs. Plenty of business-to-business sole traders register voluntarily below the threshold for exactly that reason.
If your customers are consumers — trades, salons, food, tutoring, most local services — VAT is a genuine 20% price rise or a genuine cut to what you keep. There is no third option.
Year one, below the line: turnover £89,000. She keeps £89,000 of customer money before her costs.
Year two, over the line: turnover £96,000 at the same prices. She is now registered.
• Output VAT: £96,000 ÷ 6 = £16,000 (the VAT fraction of a VAT-inclusive price is one sixth).
• Input VAT reclaimed on £7,200 of products and consumables: £1,200.
• Net VAT paid to HMRC: £14,800. Customer money retained: £81,200.
She turned over £7,000 more and ended up £7,800 worse off. That is the cliff, in one line. To stand still on the same net income she would have to charge £115,200 gross — a full 20% rise against unregistered competitors doing the same job.
This is why you see capable consumer-facing businesses sitting at £86,000 for years. It is not a lack of ambition. It is arithmetic, and it is rational right up until the point you are big enough to grow through it.
The Flat Rate Scheme: a real saving for some, a trap for others
You can join the Flat Rate Scheme if your VAT-exclusive taxable turnover is £150,000 or less. You charge customers the normal 20%, but pay HMRC a flat percentage of your VAT-inclusive turnover and give up the right to reclaim input VAT on most purchases. There is a 1% discount in your first year of VAT registration.
The published rates vary by trade. Hairdressing and beauty is 13%. General building and construction is 9.5%. Management consultancy is 14%. Computer and IT consultancy is 14.5%. Business services not listed elsewhere is 12%.
• Standard VAT accounting: £14,800 (as above).
• Flat Rate Scheme at 13%: £96,000 × 13% = £12,480.
• Flat Rate Scheme in year one at 12%: £11,520.
The scheme saves her £2,320 a year, and £3,280 in the first year. The bookkeeping is also markedly simpler.
Now the trap. If your spending on goods is less than 2% of your turnover, or less than £1,000 a year, you are a "limited cost business" and your rate is 16.5% regardless of trade. Goods means physical items — not subcontractors, not software, not rent, not accountancy, not fuel in most cases.
• Flat Rate Scheme: £92,000 × 16.5% = £15,180.
• Standard VAT accounting: output VAT £92,000 ÷ 6 = £15,333, less input VAT reclaimed on goods and on services such as software, insurance and professional fees.
On goods alone she saves £153 by using the scheme. Reclaim just £200 of VAT on software and subscriptions under standard accounting and the scheme is already costing her money. For most low-cost service businesses the Flat Rate Scheme is the wrong answer, and the 16.5% rate is why.
Two other schemes worth a decision, not a default
Cash accounting. You can join if your taxable turnover is £1.35 million or less. You account for VAT when money actually moves rather than when invoices are raised, so you never pay HMRC VAT on an invoice your customer has not settled. For any sole trader with slow payers this is the single most valuable choice on the list — and it pairs naturally with the discipline in our post on getting paid faster.
Annual accounting. One return a year with interim payments on account. It smooths the admin but delays the reckoning; most one-person businesses are better served by quarterly returns and an accurate picture.
Whichever you choose, VAT returns are filed under Making Tax Digital using compatible software. Every VAT-registered business is inside MTD for VAT already, and Making Tax Digital for Income Tax is a separate obligation arriving on its own timetable — from 6 April 2026 for sole traders with qualifying income over £50,000, from 6 April 2027 at £30,000 and from 6 April 2028 at £20,000. Our MTD guide for sole traders sets out which of the two you are in and when.
What late registration actually costs
Register late and HMRC registers you from the date you should have been registered. You then owe the VAT on every sale made since that date, whether or not you charged it. Going back to a domestic customer six months later to ask for another 20% is, in practice, not a conversation that succeeds — so it comes out of your own pocket.
On top of the VAT there is a failure-to-notify penalty, charged as a percentage of the tax you failed to declare. For a non-deliberate failure the range is 0% to 30% if you tell HMRC yourself within 12 months of the tax becoming due, and 10% to 30% if they have to prompt you. Leave it longer than 12 months and the unprompted range starts at 10% and the prompted range at 20%. Deliberate failures run from 20% to 70%, and deliberate and concealed failures from 30% to 100%. Late-payment interest runs on top.
• VAT now due: £30,000 ÷ 6 = £5,000, none of it collected from customers.
• Failure-to-notify penalty, non-deliberate and prompted, within 12 months: 10% to 30% of £5,000 = £500 to £1,500.
• Plus interest on the unpaid VAT.
A worst case near £6,500, none of which buys anything. The unprompted range starting at 0% is the entire argument for telling HMRC the moment you spot it rather than hoping.
Coming back down: the £88,000 deregistration threshold
The exit is not the same number as the entrance. You can ask HMRC to cancel your registration once your taxable turnover falls below £88,000, or if you can show it will fall below that over the next twelve months. The £2,000 gap between the two figures exists deliberately, so a business hovering at the line does not register and deregister in alternate months.
Deregistering is not free. You may owe VAT on stock and assets still on hand where you reclaimed VAT when you bought them, so it is worth running the numbers before you apply rather than after.
What to do this week
- Work out your rolling twelve-month figure today. Add up taxable sales for the last twelve complete months. Write it down. That single number is the whole game.
- Project it forward six months using your booked work. If it crosses £90,000, you now know the month, which means you get to choose how you handle it.
- Decide which side of the line you are optimising for. Staying under means capping growth deliberately, which is a legitimate choice. Crossing means planning to be a £120,000-plus business where the maths works again, rather than stalling at £92,000 with all of the VAT and none of the scale.
- Price the schemes before you need them. Run your own numbers through the Flat Rate calculation above, including the 16.5% limited cost test, and check whether cash accounting suits your payment terms.
- Set a monthly reminder to re-check the rolling number. It is a five-minute job that prevents a four-figure penalty.
One thing that does not work
Splitting a business in two to stay under — you take the weekday work, your partner takes the weekend work, same trade, same van, same customers — is disaggregation. HMRC can direct that the businesses be treated as a single taxable person and register you from the date the combined turnover crossed. Genuinely separate trades with separate customers, premises, bank accounts and books are fine. Artificially separated ones become expensive, and the penalty band for a deliberate failure starts at 20%.
Everything above comes down to one habit: knowing your rolling twelve-month number before it knows you. For our clients that is a dashboard glance, with a flag well before the line, plus the registration, the scheme choice and the quarterly returns handled when the day comes — all inside the Grow package at £39 + VAT a month. If you are approaching the threshold and want the decision made with the numbers in front of you, get started.
