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Understanding Your UK Tax Numbers: UTR, NI Number, and More

Tax & HMRC
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When you start a business in the UK, you will quickly come across a lot of official-looking reference numbers. From your UTR to your National Insurance number, it can be confusing to know what they all mean, who issues them, and when you need to use them. It is completely normal to feel a little unsure about this at first.

This guide is written to calmly explain the most common tax and business numbers you will encounter. We will look at what each one is for, who has one, and where you can find it. Understanding these numbers is a small but important step in managing your business with confidence.

The Key UK Business and Tax Numbers

Think of these numbers as official identifiers for you and your business. HM Revenue & Customs and Companies House use them to make sure they are dealing with the right person or company. Here are the main ones you should know about.

First is the Unique Taxpayer Reference (UTR). A 10-digit number from HMRC that acts as your main reference for the tax system. Sole traders get a personal UTR, while limited companies get their own Company UTR.

Next is your National Insurance (NI) Number, which everyone who works in the UK has. This is for the National Insurance system, which funds state benefits, and it looks something like QQ 12 34 56 A.

If you have a limited company, you will also have a Company Registration Number (CRN). This is an 8-character number issued by Companies House when your company is incorporated. Sole traders do not have one.

For businesses registered for VAT, HMRC issues a 9-digit VAT Registration Number (VRN).

Finally, if you employ people, you will receive both a PAYE Reference Number for managing payroll with HMRC and a PAYE Accounts Office Reference Number used specifically for making payments to HMRC for PAYE.

UTR: The Most Important Tax Number

Your Unique Taxpayer Reference (UTR) is probably the most important tax number you will have. It is how HMRC identifies you for all things related to your tax returns.

  • If you are a sole trader, you will use your personal UTR on your Self-Assessment tax return (SA100).
  • If you run a limited company, the company itself has a UTR for its Corporation Tax returns (CT600s), and you (as a director) will also have your own personal UTR if you need to file a Self-Assessment return for other income, such as taking dividends from your limited company.

It is a common point of confusion, but it is helpful to remember that a limited company is a separate legal entity with its own tax identity.

Companies House Authentication Code

(Limited Companies, Limited Liabilities Partnerships Only)

Upon registering your limited company or LLP, you will receive a 6 character Companies House Authentication Code. This code is required in order to submit your annual Companies House Confirmation Statements, or if you ever need to add and appoint new directors, shareholders or create new share classes or split shares.

If you ever lose your Companies House Authentication Code, you can request for this to be reposted out to you. However this can only be posted out to the company’s registered office address!

Companies House Personal Code – For Directors and PSCs of  Limited Companies and LLPs

As of 18th November 2025, new legislation has come into force. This requires all directors and PSCs of limited companies and partners of LLPs to complete a one time ID verification with Companies House and having a unique Companies House Personal Code. This new Personal Code is unique to individuals and only one will be issued and is to aid Companies House with linking directors and PSCs to companies. E.g if  a director is a director of  multiple companies, this Companies House Personal Code is used as an identifier to link the individual to all of the companies that they are associated with.

The code that is issued will be in the format of the following: XXX-XXXX-2223

Please note, that from the 18th November 2025, if an individual is trying to set up a limited company. The one time CH ID Verification check will  need to be completed beforehand, and their Companies House Personal Code issued before their company can be incorporated.

The Companies House Personal Code is used for the following purposes:

  • To be able to submit Companies House Confirmation Statements to Companies House (In conjunction with their Companies House Authentication Code)
  • To add an individual as a director or partner of  a limited company or LLP
  • To add an individual as a PSC of a limited company or LLP
  • In order to incorporate a new limited company / LLP.

    If you have lost your Companies House Personal Code, you can retrieve this by the following:
  • Searching your emails from ‘Companies House’ with registered email address that was used when the Companies House ID Verification Check was completed
  • Contact your ACSP (Authorised Corporate Service Provider) who completed the ID Verification Check for you
  • Check your Companies House Web-Filing Account

Where to Find Your Numbers

Knowing what these numbers are is one thing; finding them is another. Here is a quick guide to where you can usually locate them:

  • UTR: On any letters or notices from HMRC about your tax return, or in your online HMRC account (Government Gateway or Gov.One Account.)
  • NI Number: On your payslips, P60, or any letters from HMRC or the Department for Work and Pensions (DWP).
  • Company Registration Number (CRN): On your certificate of incorporation from Companies House and on the public register at Companies House.
  • VAT Number: On your VAT registration certificate from HMRC.

It is a good idea to keep a secure record of these numbers somewhere safe. You will need them regularly when dealing with HMRC or setting up business accounts.

When Getting Advice Can Help

While you are not required to use an accountant to manage your business administration, it can be helpful to get advice if you are unsure which numbers apply to you or if you are having trouble finding them. This is especially true when you are setting up a business for the first time.

If you would like calm, practical support as your business develops, Penney’s Accountancy works with UK small businesses in Farnborough and the surrounding areas, helping owners understand their responsibilities and make confident decisions at every stage.

Want to Learn More in Your Own Time?

For those who want to build their confidence and understand these topics in more detail, Penney’s Finance School offers an online, self-paced business and finance course. It covers everything from company setup to cash flow and tax, allowing you to learn at your own pace.

Important information

The information provided in this article is intended as general guidance for UK businesses only and reflects UK tax legislation and HMRC guidance as of February 2026.

Tax rules and business requirements can change, and individual circumstances vary. Before acting on any of the information above, we recommend speaking to a qualified accountant who can provide advice tailored to your specific situation.