When your business has to register for VAT

VAT registration is the first tax milestone most growing businesses hit, and the rule that trips people is not the threshold itself. It is the period the threshold is measured over.

The threshold and the two tests

The threshold is £90,000 of taxable turnover. GOV.UK sets out the backward-looking test as your "total taxable turnover for the last 12 months goes over £90,000 (the VAT threshold)".

There is also a forward-looking test, which is the one that surprises people: you must register if you "expect your taxable turnover to go over £90,000 in the next 30 days". That can be triggered by a single large contract, before you have invoiced anything.

"The last 12 months" is a rolling window

This is the heart of it. The twelve months is not your accounting year and does not reset in April. It rolls. At the end of every month you look back over the previous twelve and ask whether the total crossed £90,000.

So a business billing £7,000 a month sits just under £84,000 a year and never registers. The same business with two unusually good months can cross the line in, say, the twelve months ending in August, even though neither its financial year nor any single quarter looked remarkable. If nobody is watching the rolling total, the first anyone notices is after the obligation has already arisen.

Taxable turnover is also not simply everything that lands in the bank. It is the value of the goods and services you supply that are not exempt. Which of your income streams count is worth establishing once, properly, rather than assuming.

What changes when you register

Three things, in descending order of how much they will occupy you.

You start charging VAT on your taxable sales, which means deciding whether to add it to your prices or absorb it. For a business selling to VAT-registered companies this is close to neutral, because your customers reclaim it. For one selling to the public it is effectively a price rise or a margin cut, and it is better to decide which deliberately than to discover it in your first quarter.

You can reclaim VAT on what you buy. For a business with real equipment, stock or premises costs, that is money back, and it is why some businesses register before they have to.

You take on returns. VAT-registered businesses keep digital records and file through Making Tax Digital using compatible software, on a regular cycle. This is bookkeeping discipline rather than difficulty, but it is a standing commitment.

Registering early on purpose

Voluntary registration below the threshold is legitimate and sometimes sensible. It suits businesses whose customers are mostly VAT-registered, and businesses with significant input costs to reclaim. It suits a consumer-facing business with thin margins much less well.

A quieter reason some London business-to-business firms register early: an invoice with a VAT number on it reads as an established business to procurement departments. That is a commercial judgement rather than a tax one, but it is a real consideration.

The mistakes that cost money

Watching the financial year instead of the rolling twelve months is the common one. Ignoring the 30-day forward test when a large contract is signed is the expensive one. Assuming that because you are under the threshold today you have a year's grace is the one that produces backdated liability, because the obligation runs from when the test was met, not from when you noticed.

If you are within about £15,000 of the threshold on a rolling basis, put the rolling total on your monthly numbers. It is a single line, and it is the line that decides this.

How we checked this

Facts in this piece were taken from the primary sources below and checked on 6 October 2026. Rules and figures change: check the source before you act on anything here.

• GOV.UK: VAT registration — when to register, the source of the £90,000 threshold and both tests quoted above