How to Number Invoices in the UK: HMRC and GOV.UK Rules

What GOV.UK and HMRC actually say about invoice numbers, word for word: VAT and non-VAT invoices, letters, starting numbers, several series, gaps and credit notes. Every quote links to its source and was last verified on .

Quick answer

In practice: give every invoice its own number, keep each series running in order, and never reuse a number. Letters, a starting number above 1 and more than one series are all accepted by HMRC’s internal guidance, as quoted below.

If you are not VAT-registered

The GOV.UK list of what an invoice must include starts with a unique identification number. That list covers all invoices, VAT-registered or not. It asks for a number that is unique; the words “sequential … series” come from the VAT rules in the next section.

A simple running series such as INV-0001, INV-0002 and so on is one easy way to keep every number unique. The rest of the GOV.UK list (your details, the customer’s, dates, amounts, and the extra lines for sole traders and limited companies) is on the GOV.UK page.

Source: GOV.UK, Invoicing and taking payment from customers: Invoices - what they must include · official guidance · last verified

If you are VAT-registered: which VAT invoices need a number?

HMRC’s list for a full VAT invoice starts with the number. The lists HMRC gives for simplified and retailers’ VAT invoices (£250 or less) have no number item. VAT Notice 700 and VAT Notice 700/21 word the £250 rules differently, so each is shown in its own row.

Invoice typeDoes HMRC’s list include a number?Verbatim lineSource
Full VAT invoice Yes You must show the following details on any VAT invoice you issue: a sequential number based on one or more series which uniquely identifies the document VAT Notice 700, paragraph 16.3.1 (first item)HMRC notice · last verified
Full VAT invoice Yes You must show the following details on any VAT invoices you issue: a sequential number based on one or more series which uniquely identifies the document VAT Notice 700/21, section 4.1 (first item)HMRC notice · last verified
Simplified VAT invoice No number item in the list You can issue a simplified invoice if all of the following conditions exist: the value of the supply you are making is £250 or less; your customer agrees; if your business is based in Northern Ireland your customer must not be from an EU member state. The simplified invoice must include: your name, address and VAT registration number; the time of supply (tax point); a description which identifies the goods or services supplied; for each applicable VAT rate, the total amount payable, including VAT, and the VAT rate VAT Notice 700, paragraph 16.6.1HMRC notice · last verified
Retailers’ VAT invoice No number item in the list The retailers’ VAT invoice must include: your name, address and VAT registration number; the time of supply (tax point); a description which identifies the goods or services supplied; for each applicable VAT rate, the total amount payable, including VAT, and the VAT rate … You must issue a full VAT invoice if the transaction is for: more than £250; £250 or less but the customer requests one VAT Notice 700, paragraph 16.6.2HMRC notice · last verified
Retailer, asked for an invoice: £250 or less No number in the list £250 or less (including VAT), then you can issue an invoice showing your name, address and VAT registration number, the time of supply (tax point), a description which identifies the goods or services supplied, and for each VAT rate applicable, the total amount payable, including VAT shown in sterling and the VAT rate charged VAT Notice 700/21, section 4.4HMRC notice · last verified
Retailer, asked for a VAT invoice: more than £250 A full VAT invoice: yes (see the first rows). This section does not list the details of a modified VAT invoice. more than £250 and you’re asked for a VAT invoice, then you must issue either a full VAT invoice or modified VAT invoice, showing VAT inclusive rather than VAT exclusive values VAT Notice 700/21, section 4.4HMRC notice · last verified
Not a retailer: £250 or less No number in the list £250 or less (including VAT), then you issue an invoice showing your name, address and VAT registration number the time of supply (tax point), a description which identifies the goods or services supplied, and for each VAT rate applicable, the total amount payable, including VAT shown in sterling and the VAT rate charged VAT Notice 700/21, section 4.5HMRC notice · last verified
Not a retailer: more than £250 A full VAT invoice: yes (see the first rows). This section does not list the details of a modified VAT invoice. more than £250, then you must issue either a full VAT invoice or a modified VAT invoice, showing VAT inclusive rather than VAT exclusive values VAT Notice 700/21, section 4.5HMRC notice · last verified

List items are joined with semicolons here; “…” marks text left out. This section covers the number only, not every detail a VAT invoice must show. For the full VAT picture, see our VAT and GST invoicing guide and HMRC’s VAT Notice 700, section 16.

Letters, starting number and several series

HMRC’s internal manual VATREC5010 answers the common questions about the VAT invoice number. Questions and answers are quoted as published.

Letters in the numberDoes the invoice number series have to be numerical, or can it include letters?
The ‘invoice number’ can be numerical, or it can be a combination of numbers and letters, as long as it forms part of a unique and sequential series.
Starting at a number other than 1In order to avoid the appearance of having only just started in business I do not want to start at Invoice no.1 and would prefer to commence with, say, Invoice no 1135. Is this allowed?
Yes, as long as the invoice series runs consecutively from that point.
A customer reference plus a consecutive numberI currently use a unique customer reference number as the identifying number on the invoice. If I add an additional consecutive number will this be acceptable ?
Yes, this would have the affect of creating a unique and sequential series. [sic, as published]
Several series for several customersI have several customers and I wish to run several separate sequences of invoices at the same time. Is this possible?
Yes, it is acceptable to operate more than one sequence at the same time.
A series for each unit or divisionMy business operates as several separate business units or divisions. Is it possible for each unit or division to operate its own sequence of invoices?
Yes, it is acceptable to operate more than one sequence at the same time.

Source: HMRC internal manual VATREC5010 (VAT Trader Records) · HMRC internal guidance · last verified

Gaps, cancelled and spoiled invoices

A break in the sequenceWhat if there is a break in sequence, for example where I cancel an invoice or it is spoiled and never issued to a customer?
As long as you retain the cancelled or spoiled invoice in your accounting records, or you can provide an explanation for the break in sequence, this is acceptable.

So if you cancel an invoice, keep it (for example marked as cancelled) with your accounting records, or be able to explain the gap. Do not reuse a cancelled invoice’s number for a new invoice, because each number must uniquely identify one document.

Source: HMRC internal manual VATREC5010 · HMRC internal guidance · last verified

Credit note numbers

VAT Notice 700, paragraph 18.2.3 (valid credit notes), says a credit note must show clearly, among other details:

  • the identifying number and date of issue
  • the number and date of the original VAT invoice or invoices relating to the supply

We found no HMRC text that requires a separate series for credit notes, so a separate series such as CN-2026-001 (the number our credit note generator pre-fills) is an option, not a rule.

Source: VAT Notice 700, paragraph 18.2.3 · HMRC notice · last verified

Examples

NumberTypeWhy it fits
Sales invoice No. 174Official (HMRC)The heading of HMRC’s worked example in VAT Notice 700, paragraph 16.7 (“Example of a completed VAT invoice”). VAT Notice 700/21, section 4.3 uses “Sales invoice no 174”.
INV-0001, INV-0002, INV-0003IllustrativeLetters and numbers in one series: VATREC5010 accepts “a combination of numbers and letters, as long as it forms part of a unique and sequential series”.
1135, 1136, 1137IllustrativeStarting above 1: “Yes, as long as the invoice series runs consecutively from that point.” (VATREC5010)
SHOP-2026-0001 and WEB-2026-0001IllustrativeOne series per unit or division, running at the same time: “it is acceptable to operate more than one sequence at the same time.” (VATREC5010)
CN-2026-001IllustrativeA credit note with its own number, which must also show the number and date of the original VAT invoice (VAT Notice 700, 18.2.3). A separate CN- series is an option, not a rule.

Create a UK invoice

In our VAT invoice generator, the Invoice # field is free text, up to 50 characters, pre-filled with the sample number VAT-2026-001 for you to replace. Nothing auto-increments, so keep a note of the last number you issued.

Frequently asked questions

Do UK invoices need a number?

Yes. GOV.UK says: “Your invoice must include: a unique identification number”. For a VAT invoice, HMRC asks for “a sequential number based on one or more series which uniquely identifies the document” (VAT Notice 700, paragraph 16.3.1, and VAT Notice 700/21, section 4.1; the same words are in the VAT Regulations 1995, regulation 14(1)(a)).

Can a UK invoice number contain letters?

Yes. HMRC’s internal manual VATREC5010: “The ‘invoice number’ can be numerical, or it can be a combination of numbers and letters, as long as it forms part of a unique and sequential series.”

Can I start my invoice numbers at a number other than 1?

Yes. Asked about starting at Invoice no 1135 instead of 1, HMRC’s internal manual VATREC5010 answers: “Yes, as long as the invoice series runs consecutively from that point.”

What if there is a gap in my invoice numbers?

HMRC’s internal manual VATREC5010, on a cancelled or spoiled invoice: “As long as you retain the cancelled or spoiled invoice in your accounting records, or you can provide an explanation for the break in sequence, this is acceptable.”

Does a simplified VAT invoice need a number?

The list in VAT Notice 700, paragraph 16.6.1, has no number item. It says a simplified invoice must include: “your name, address and VAT registration number”, “the time of supply (tax point)”, “a description which identifies the goods or services supplied” and “for each applicable VAT rate, the total amount payable, including VAT, and the VAT rate”. You can issue one only if “the value of the supply you are making is £250 or less” and “your customer agrees” (plus a Northern Ireland condition).

What number goes on a credit note?

Its own number and the original invoice’s number. VAT Notice 700, paragraph 18.2.3, says a valid credit note must show “the identifying number and date of issue” and “the number and date of the original VAT invoice or invoices relating to the supply”. We found no HMRC text that requires a separate series for credit notes, so a CN- series is an option, not a rule.

Sources and last verified

General information, not legal or tax advice. For rules in other countries, see the invoice numbering rules by country.