When do I have to register for VAT?
The answer almost never depends on your tax year, and that is the part most people get wrong. Here is how the test actually works, and the two ways it can catch you.
Most people asking this question are looking for a number. The number matters less than the period it is measured over, and that is where the surprise usually comes from.
It is a rolling twelve months, not your accounting year
The registration test looks at your taxable turnover over any twelve consecutive months. Not your financial year. Not the tax year. Any twelve in a row, recalculated at the end of every month.
So a business that earns most of its money between September and January can cross the threshold in February while its year-to-date figure still looks comfortable. The twelve months being measured are March to February, and nobody was looking at them.
The second test is forward-looking, and it is faster
There is a separate rule for when you expect to cross the threshold within the next thirty days on its own. One large contract can trigger it. The deadline for this one runs from the moment you realised, not from the end of a month — which means signing a big job can put you in a registration deadline the same week.
What you actually have to do, and when
- Backward test: register by the end of the month following the month you crossed. You become VAT-registered from the first of the month after that.
- Forward test: register before the end of that thirty-day period, and you are registered from the date you realised.
Registering before you have to
Voluntary registration is common and often sensible. If your customers are themselves VAT-registered businesses, the VAT you charge costs them nothing and you can reclaim the VAT on what you buy. If your customers are the public, the same decision makes you either 20% more expensive or 20% less profitable, and there is no version where it is free.
The mistake that costs money
Registering late does not mean you start charging VAT late. It means you owe VAT on sales made since the date you should have been registered — sales where you did not charge it and usually cannot go back and ask for it. The penalty is a percentage on top. This is the single most expensive administrative mistake a small business in the UK routinely makes, and it is entirely avoidable by checking a rolling twelve-month figure once a month.
The current threshold figure is on gov.uk, which is the only place worth reading it from — it changes.
This is general information about how a process works, not advice about your situation. Thresholds, fees and deadlines change — check the official source linked above for the current figures, or ask a professional who can see your circumstances.