The rule, precisely
You must register for VAT when your taxable turnover passes £90,000 in any rolling 12 months — not your accounting year, not the calendar year, a rolling window you should check monthly. You must also register immediately if you expect to pass £90,000 in the next 30 days alone (the big-contract trap that catches startups signing their first serious deal).
Miss the moment and HMRC registers you from the date you crossed, meaning you owe VAT on sales where you never charged it — straight out of your margin, plus penalties.
But the more interesting question for startups is whether to register before you must. The answer is pure arithmetic about who your customers are — and the full guide runs it, plus the scheme choice that changes your cashflow.
Voluntary registration: the two-question test
Q1: Are your customers VAT-registered businesses? If yes, they reclaim every penny of VAT you charge — your price is effectively unchanged to them, and you get to reclaim VAT on your own costs (laptops, software, professional fees, and pre-registration purchases: goods up to 4 years back, services 6 months). Voluntary registration is usually free money. It also stops broadcasting “we're under £90k” to clients.
Q2: Are your customers consumers? Then VAT is a real 20% price rise (or a 16.7% margin cut if you absorb it). Stay unregistered as long as the law allows, and plan for the cliff — some businesses even manage growth timing around it.
Mixed customer base? Weight it by revenue. Mostly-B2B with some consumers usually still says register.
Choosing a scheme
- Standard VAT: charge 20%, reclaim input VAT, file quarterly. Default and correct for most.
- Cash accounting (turnover under £1.35m): you pay HMRC when customers actually pay you, not when you invoice. If clients pay slowly, this is a straightforward cashflow win with no downside for most startups — the setting most founders don't know exists.
- Flat Rate Scheme (turnover under £150k): pay a fixed percentage of gross turnover, reclaim nothing (bar capital assets over £2,000). Simpler, occasionally profitable — but the 16.5% “limited cost trader” rate kills the benefit for service businesses with few costs. Run the numbers before choosing; many startups on FRS after 2017 shouldn't be.
Cashflow rule of thumb The VAT in your bank account was never yours. Move it to a separate pot (Mettle pots do this neatly) the moment invoices are paid, and the quarterly bill becomes a non-event.
Filing: Making Tax Digital
All VAT returns must be filed through MTD-compatible software with digital records — no typing totals into a website. FreeAgent (included free in every one of our packages) keeps the digital records as a by-product of normal bookkeeping and files the return itself. Registered clients: we check and file every quarter as standard.
Startup-specific wrinkles
- Pre-registration VAT: reclaim VAT on goods bought up to 4 years pre-registration (still owned) and services up to 6 months — commonly worth four figures. Keep every receipt from day zero.
- Digital services abroad: selling to EU consumers can create VAT obligations there (OSS schemes) regardless of UK thresholds — ask before you scale internationally.
- Northern Ireland: goods trade runs under Windsor Framework rules with EU-facing quirks — specialist territory we cover as standard.
