What is VAT registration threshold?

You must register for VAT when your taxable turnover across any rolling 12 months goes over £90,000, or when you expect to pass £90,000 in the next 30 days on its own.

The rolling part is what catches people. It is not measured against your tax year or your accounting year; it is any twelve consecutive months, checked continuously. A strong autumn can push you over on a date nobody was watching for.

Once you cross it you have 30 days from the end of that month to register. The deregistration threshold is lower, at £88,000, so a business that dips slightly below is not forced straight back out.