Somewhere around £85–90k of turnover, a strange thing happens to growing sole traders: the reward for success is a 20% price rise or a 16.7% margin cut. Welcome to the VAT cliff — the sharpest edge in the UK tax system for one-person businesses, and the least warned-about.

How people actually get caught

The threshold is £90,000 of taxable turnover in any rolling 12 months — not your tax year, not a calendar year. It moves every month, which is exactly why people miss it: a strong November plus a big January job and the trailing twelve quietly crosses in February while you're busy working. You must register within 30 days of the end of the month you crossed; miss it and HMRC registers you from the date you should have been registered — you owe VAT on sales where you never charged it, straight out of your pocket, plus penalties. There's also the 30-day forward test: expect to cross £90k in the next 30 days alone (one huge contract) and you must register immediately.

What crossing actually costs

If your customers are VAT-registered businesses: almost nothing — they reclaim what you charge, and you start reclaiming VAT on your own costs. Crossing is fine; some businesses register voluntarily before they must.

If your customers are consumers (trades, salons, food, most local services): VAT is a real price rise. Either your prices jump 20% against unregistered competitors, or you hold prices and hand over a sixth of your revenue. This is why you see businesses hovering just under the threshold for years.

Strategies that work (and one that doesn't)

  • Watch the rolling number monthly. FreeAgent shows it; our clients get flagged well before the line. No ambush, ever.
  • If you'll cross, cross deliberately: register at a moment you choose, reprice with notice, and pick the right scheme — cash accounting for cashflow, and check whether the Flat Rate Scheme helps or (for low-cost service trades) hurts.
  • Grow through the cliff, not up to it. The worst place to sit is £91k — all of the VAT, none of the scale. If you're crossing, plan to be a £120k+ business where the maths works again.
  • What doesn't work: artificial splitting. Running "two businesses" (you and your partner, same trade, same van) to stay under is aggregation territory — HMRC combines them and backdates. Genuine separate trades are fine; disguised ones get expensive.

The whole trap is avoidable with one habit: knowing your rolling 12-month number. That's a dashboard glance for our clients — along with the registration, scheme choice and quarterly returns when the day comes, all inside the Grow package at £39 + VAT.