A sole trader invoice is the simplest kind there is, and the requirements are lighter than most people expect. You are not a company, so there is no company number to quote, and if you are below the VAT threshold there is no VAT to show either.
What people get wrong is the opposite of over-complicating it. They leave off the things that actually matter: a clear trading name, a real address, an invoice number that means something, and a due date rather than a hopeful "payment on receipt".
If you are registered for VAT, the rules change materially and you need the VAT template instead, because a VAT invoice has specific mandatory contents.
If you trade as something other than your own name, show both: "Jane Smith trading as Smith Joinery".
A real correspondence address. This is a legal requirement for a sole trader, not a formality.
The business being billed, spelled as it is registered.
Sequential. It is how both of you refer to this specific piece of work later.
When you sent it, and when the work was done.
Enough that someone who was not there can tell what was bought.
A specific due date, plus how to pay.
Sole traders do not have one. Inventing a reference or borrowing a UTR onto the invoice creates confusion rather than credibility.
Charging or displaying VAT while unregistered is a serious problem, not a presentational one. If you are not registered, there is no VAT line at all.
It is not a date, so it cannot be late, which makes it very hard to chase. Give a specific due date instead.
Your name and any trading name, your address, the client's name and address, a unique sequential invoice number, the date of issue, the date the work was supplied, a clear description of the work, the amount due and how to pay. If you are not VAT registered there is no VAT line and no VAT number.
No. Company numbers apply to limited companies registered at Companies House. As a sole trader you do not have one, and there is nothing to put in its place. Your name and address are the identifying details that matter, and your UTR belongs on your tax return rather than on invoices to clients.
Only if you are VAT registered, which is compulsory above the registration threshold and optional below it. Showing VAT on an invoice when you are not registered is treated seriously by HMRC, so if you are unsure whether you are registered, check before you send anything with a VAT line on it.
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