Quick answer: An Employer Reference Number (ERN) is a unique code that HMRC assigns to your business when you register for Pay As You Earn (PAYE). You’ll need it to run payroll, file tax returns, buy employers’ liability insurance, and help employees access benefits like Universal Credit. It typically looks something like 123/A45678.
If you employ staff – even just one person – there’s a good chance your business has an ERN. But many small business owners don’t know what it is, where to find it, or why it matters.
This guide covers everything you need to know about Employer Reference Numbers: what they are, when you need one, how to get one, and what to do if something goes wrong.
What is an Employer Reference Number?
An Employer Reference Number is a unique code that HMRC gives your business when you register for PAYE. It’s sometimes called a PAYE reference number or employer PAYE reference.
HMRC uses your ERN to identify your business for employment and tax purposes. Think of it as your business’s ID number for anything payroll-related.
What does an ERN look like?
An ERN has two parts: a three-digit HMRC office number, followed by a reference unique to your business. It looks something like this:
- 123/A45678
- 123/AB45678
The format can vary slightly, but you’ll always see two sections separated by a forward slash.
Where can I find my ERN number?
Employers can find their ERN in several places, such as:
- HMRC correspondence – when you first register as an employer with HMRC, you’ll receive a confirmation letter and welcome pack. Both of these will include your ERN, usually in the top right hand corner. It’s sometimes labelled as an ‘employer PAYE reference’
- employer forms – ERNs are included on forms such as P11Ds, P45s, and P60s
- payslips – any payslip generated by your payroll software should include your ERN
- HMRC online account – log in to find your PAYE reference number, along with any emails from HMRC about PAYE
Why and when do you need an ERN number?
Your ERN comes up more often than you might expect. Here are the three most common situations where you’ll need it.
1. Running payroll and filing tax returns
You can’t submit end-of-year returns without an ERN. It’s included in every full payment submission you make to HMRC. Missing or incorrect ERNs are one of the most common reasons end-of-year returns get rejected – so it’s worth keeping yours somewhere easy to find.
You’ll also need to include your ERN when submitting payroll records to HMRC for Statutory Sick Pay (SSP) requests. Employees now have access to SSP from their first day of employment.
And while you can technically run payroll and pay your staff before receiving your ERN, you’ll need to store any records and submit a late Full Payment Submission (FPS) to HMRC once the ERN arrives.
2. Employee documentation
Your employees may ask for your ERN when they need to fill in forms for the Student Loans Company or apply for Universal Credit or tax credits. It’s worth having it ready, as requests can come at short notice.
3. Buying employers’ liability insurance
If you employ people, employers’ liability insurance is usually a legal requirement. Your insurer will ask for your ERN when you buy the policy. This is a Financial Conduct Authority (FCA) requirement – it lets the insurer track your policy if a claim is made in the future.
Why do I need to give my ERN to my insurer?
The Employers’ Liability Tracing Office (ELTO) runs a database that helps employees trace their past employers’ insurers – making it easier to make an employers’ liability claim.
Your ERN is central to this process. If a former employee develops an illness linked to workplace exposure and makes a claim against your business, using ERNs, the ELTO can identify everywhere that person has worked. This helps establish who is actually liable for the claim.
If you have a Simply Business policy with us, please submit your employer PAYE reference number (ERN) if you haven’t already.
Staying on top of your employer responsibilities
Your ERN is just one piece of the puzzle when it comes to managing your employer responsibilities. Alongside keeping your PAYE registration up to date, you’ll also need to make sure your employers’ liability insurance is in place – and that your insurer has your ERN on file.
If you have a Simply Business policy, make sure you’ve submitted your employer PAYE reference number so your cover is properly recorded.
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How to get an ERN in the UK
You get your ERN when you register as an employer with HMRC. Here’s how the process works depending on your business type.
Limited companies with up to nine directors can register as an employer online. You’ll answer some questions about your business, then sign in to your Government Gateway account to complete the registration.
Sole traders, partnerships, or businesses working under the Construction Industry Scheme (CIS) may be able to register online. However, in some circumstances you may have to register by phone.
Whichever route you take, you must register before your employee’s first payday. You can’t register more than two months in advance.
HMRC will send your ERN in a letter after you register.
What if I need to pay someone before my ERN arrives?
If you need to pay someone before you get your ERN, you can:
- run payroll
- store the full payment submission
- send a late full payment submission to HMRC once you have your ERN
Common ERN issues and how to fix them
What if I’ve lost my ERN number?
Check any letters or emails from HMRC about PAYE – your ERN will be there. It also appears on P45s and P60s for current and previous employees.
If you can’t find it anywhere, it’s possible you haven’t registered as an employer yet. If you’re employing someone (or planning to), you should register as soon as possible.
What if there’s a delay in receiving my ERN?
Delays are often common, so sometimes a short wait is normal. If the wait is longer, you can check your registration status on HMRC’s online portal. Alternatively, call HMRC’s PAYE helpline on 0300 200 3200.
What if my ERN details are incorrect?
Contact HMRC with the correct information as soon as you notice the error. Fixing it quickly avoids payroll problems further down the line.
ERN vs Accounts Office reference number – what’s the difference?
These two numbers are easy to mix up because both can appear on payslips and payment letters.
- your ERN identifies your business’s PAYE registration
- your Accounts Office reference number tracks payments you make to HMRC’s accounts office
They serve different purposes, so make sure you’re using the right one for the right task.
ERN vs unique taxpayer reference (UTR) number
A UTR number is another HMRC identifier, but it has nothing to do with PAYE. UTR numbers relate to Self Assessment tax returns. If you’re filing payroll information, you need your ERN – not your UTR.
How HMRC uses your ERN
While you use your ERN primarily for payroll and insurance, HMRC uses it for a few different purposes:
- tax collection – to identify your business when you pay income tax and National Insurance through PAYE
- linking PAYE schemes – if your business operates from multiple locations, or is merged with or acquired by another business
- compliance monitoring – to track your business’s payroll and tax history
What are the exceptions to PAYE?
Not every business needs to register for PAYE – and if you don’t register, you won’t have an ERN.
You don’t need to register for PAYE if:
- your employees are self-employed or paid through an agency
- no employee earns more than the lower earnings limit (£129 in 2026-27)
- your workers are unpaid volunteers
- your business is based in the Channel Islands or the Isle of Man
If none of these apply to you, you’ll need to register for PAYE and get an ERN.
Can a business have more than one ERN?
Yes – but most small businesses will only ever have one.
Multiple ERNs tend to apply to larger businesses operating from different locations, or businesses that have merged with or been acquired by another company. If you run a single business from one location, one ERN is almost certainly all you need.
Why your ERN could become more important in the future
Because Real Time Information (RTI) requires you to submit payroll data to HMRC on or before every payday, there’s very little room for administrative slip-ups.
If you enter an incorrect ERN, or if your software rejects the submission due to mismatched employee data, the HMRC gateway will block the filing on the spot. Because the system is entirely automated, a rejected file is instantly flagged as a missed deadline – there’s no human review to catch the mistake.
While HMRC operates a ‘one free pass’ rule for your first late filing of the tax year, any subsequent automated rejections will trigger an instant penalty. For small businesses with fewer than 10 employees, these automatic fines start at £100 per month and scale up quickly for larger teams, making a simple typo a potentially expensive headache.
Employer Reference Number FAQs
What is an Employer Reference Number (ERN)?
An ERN is a unique code that HMRC assigns to your business when you register for PAYE. It’s used to identify your business for employment and tax purposes. It’s also known as an employer PAYE reference number.
Is an ERN the same as a PAYE number?
Yes, an Employer Reference Number and a PAYE reference number are the same thing. You may see it labelled differently in different places, but it refers to the same unique identifier.
Where can I find my ERN?
You can find your ERN in HMRC correspondence, on forms like P45s and P60s, on payslips generated by your payroll software, and in your HMRC online account.
What does an ERN look like?
An ERN has two parts separated by a forward slash – a three-digit HMRC office number and a business-specific reference. For example: 123/A45678 or 123/AB45678.
Do I need an ERN to get employers’ liability insurance?
Yes. If you employ people, employers’ liability insurance is a legal requirement, and your insurer will ask for your ERN when you buy the policy.
What should I do if I’ve lost my ERN?
Check any HMRC letters or emails about PAYE, or look on past P45s and P60s. If you can’t find it anywhere, contact HMRC directly or check your HMRC online account.
Can a small business have more than one ERN?
Yes, but most small businesses only have one. Multiple ERNs are more common in larger businesses with multiple locations or those that have gone through a merger or acquisition.
Do I need an ERN if I pay myself through PAYE?
Yes, even if you’re the only director and pay yourself through PAYE, you still need to register as an employer and get an ERN.
Useful guides for small businesses
- What is gardening leave? A guide for employers
- How to create an occupational health policy
- Self Assessment tax returns: a guide for the self-employed
- What does employers’ liability insurance cover?
Looking for employers’ liability cover?
As the UK’s biggest business insurance provider, we specialise in employers’ liability insurance. We’ll run you a quick, tailored quote right now online, and let you decide if we’re a good fit.