I’ve updated this post on 16 June 2020
Including an invoice number is a legal requirement for your sales invoices, whether you are self-employed, have a Limited Company and/or VAT registered or not.
What is an Invoice Number?
An invoice number is a unique set of numbers or letters (or a combination) entered onto each invoice raised.
Why Do They Matter?
Invoice numbering matters because if HMRC ever investigates your business, they will review your invoices in numerical order.
This is a check to confirm that you have included all invoices in your records and give them some assurance that you keep your accounting records in good order.
That means it is not important what number you start with, but that you run a sequential system when you raise your sales invoices.
Should I Start at Invoice Number 1?
Yes, you could simply start at sales invoice number 1 and go sequentially thereafter.
Although some businesses opt to start with something further along. That way their customers don’t know they have only just started trading.
Should I Include a Client Reference?
Some businesses opt to include a client reference as part of their numbering so they can identify invoices relating to a client or project.
For example, sales invoicing for a project with ABC Limited could begin ABC001, then ABC002.
This would allow you to check that you have invoiced correctly and in full for this project with ABC Limited.
Should I Include the Year?
Sometimes businesses use the year as the anchor reference for each invoice they raise.
So in 2019, a business may begin their invoice with 2019-01, 2019-02, 2019-03 etc.
Then in the new year begin using 2020-01, 2020-02 and so on.
Whichever method of sales invoice numbering you choose to adopt always ensure you are consistent with the referencing.
Self-Employed Invoice Template with Set-Up Guide – Use this self employed invoice template and set up guide to create on-brand invoices that you can send to your customers and clients.
New Here? Learn how to set up the financial side of your business with these easy to understand guides and resources:
- Sole Trader or Limited Company? – Download my free calculator to check which business structure would help you to pay less tax;
- Tax Records and Bookkeeping – Understand what tax records you’ll need to keep and how to set up your own bookkeeping system;
- Self Employment Taxes Explained – Learn what taxes you’ll pay, how much and when;
- VAT Guides – From registration to de-registration, VAT schemes and thresholds, these guides will take you through the basics every UK small business owner needs to know;
- Invoice Template – Free template and step-by-step guide so you can get paid by your clients.