You can register for VAT voluntarily even if your turnover is well below the mandatory threshold. Whether it saves or costs you money depends almost entirely on who your customers are and how much VAT-able expense you carry - it is a genuine calculation, not a one-size-fits-all answer.
When voluntary registration tends to help
Most of your customers are VAT-registered businesses themselves - they reclaim the VAT you charge, so your prices do not effectively rise for them
You have significant upfront costs - equipment, materials, software - where reclaiming input VAT genuinely offsets what you would pay HMRC
You want to look more established to bigger clients, some of whom assume a business without a VAT number is very small
When it tends to hurt
Most of your customers are individual consumers or non-VAT-registered businesses - they cannot reclaim the VAT, so your effective price rises by the VAT rate
Your running costs are mostly your own labour, with little VAT-able expense to reclaim against
You would rather avoid the extra admin of VAT returns while your business is still small
A worked example
A freelance consultant billing £40,000 a year, almost entirely to VAT-registered companies, with minimal expenses: registering voluntarily adds VAT to every invoice, which their clients reclaim in full, while the consultant can now also reclaim VAT on their laptop, software subscriptions and home-office costs. Net effect: close to free extra cash back, no real downside. Compare that to a wedding photographer billing £40,000 a year almost entirely to individual couples: adding VAT means either absorbing 20% of revenue as a cost, or raising prices 20% and risking losing bookings to non-VAT-registered competitors - registering voluntarily here is a real trade-off, not a clear win.
The decision in one sentence
If your customers can reclaim the VAT you would charge them, voluntary registration is usually worth it; if they cannot, it usually is not - check your actual customer mix before deciding either way, and get an accountant to run the numbers if you are close to the line.
Can I register for VAT before I reach the threshold?
Yes - voluntary VAT registration is available to any UK business, regardless of turnover, and can be a genuine financial advantage depending on your customer base.
Does voluntary VAT registration make sense for a business selling to the public?
Can I deregister from VAT later if voluntary registration turns out to be the wrong call?