Accounts Office Reference Number: A Complete UK Guide

An Accounts Office Reference Number (AORN) is a unique 13-character code HMRC uses to identify your employer PAYE scheme. You’ll usually need it when paying PAYE tax and National Insurance, setting up payroll, or contacting HMRC about your employer account.

Finding the right number can be confusing because HMRC uses many references for different purposes, and using the wrong one could delay or incorrectly allocate your payment.

This guide explains where to find your AORN, what it looks like, and when you need to use it.

Key points

• The AORN and Employer PAYE Reference are different 🔍
  Although they're issued together and look similar, they serve different purposes. Your Employer PAYE Reference identifies your PAYE scheme, and you use your AORN when sending payments to HMRC.
• Some PAYE payments use a 17-character payment reference 📝
  Your AORN is always 13 characters long, but when paying HMRC early or late, you'll need to add four extra digits to specify the correct tax year and payment period.
• Keep your AORN somewhere easy to access 📂
  You can find it on your HMRC employer registration letter, in your HMRC online account, in your payroll software, or by asking your accountant. Using the wrong reference can delay HMRC from allocating your payment.
• ANNA takes the hassle out of PAYE admin 🚀
  ANNA stores your PAYE details and helps you run payroll, file Corporation Tax and Self Assessment returns, track tax deadlines, and manage your business finances. That way, you spend less time on admin and more time running your business.

What is the Accounts Office Reference Number used for?

The AORN exists because HMRC's payment systems don't recognise your business by name, but by this code. 

HMRC runs millions of PAYE accounts at once, and each one needs to be paid separately every month. When money arrives in HMRC's bank account, the reference attached to that payment tells HMRC's systems whose PAYE bill it's clearing. 

If there’s no AORN, or if it’s the wrong one, the payment reaches HMRC but can't be matched to your scheme, so it sits unallocated.

From HMRC's side, a payment that can't be matched looks exactly the same as no payment at all. You could pay on time, in full, and still end up with a reminder letter or a penalty notice because the code attached to the transfer didn't tell HMRC to credit your business.

The Accounts Office Reference Number format

The reference always follows the same 13-character structure:

• The first three digits identify the HMRC tax office that manages your PAYE scheme
• The letter P is fixed and appears in every AORN, regardless of business type or size
• The second letter, often A, forms part of the internal coding HMRC uses to route your account within that tax office
• The final eight digits are unique to your specific payment account, and no two employers share the same combination

A typical example looks something like 123PA00012345.

You don't need to memorise what each part means to use the reference correctly, but it’s a good idea to get familiar with your AORN. This helps you spot any typos before you send a payment.

⚠️ Keep in mind

When making PAYE payments early or late, you’ll need to add four extra digits to the end of your AORN. These digits identify the tax year and payment period, helping HMRC allocate your payment correctly.

Accounts Office Reference vs Employer PAYE Reference

Many people confuse these two references because they are issued at the same time, start with the same three-digit tax office number, and relate to PAYE. 

However, they serve different purposes, and you can't use one in place of the other.

Your Employer PAYE Reference identifies your PAYE scheme. It appears on payslips, P45 forms, P60 forms, and any payroll submissions to HMRC.

Your AORN identifies your payment account, and it's only used when you're sending money to HMRC. You won't see it on a payslip, and employees never need to know it.

Payroll software usually labels each field clearly, but it’s not uncommon to mix them up when entering a payment reference manually into online banking, so be careful.

💡 Did you know? 

If you run your payroll through ANNA, your AORN gets stored against your account once. Then, ANNA applies it automatically to every PAYE payment, so you don't have to enter the code each month.

How to use your Accounts Office Reference Number when paying HMRC

Use your AORN as the payment reference whenever you send PAYE tax and National Insurance payments to HMRC. The exact payment process depends on how you pay:

• Online banking or Faster Payments: Enter your full payment reference, including any required period digits, when making the transfer
• CHAPS: Use the same reference as you would for any other payment
• Direct Debit: Your reference is linked automatically once you set up the mandate through HMRC, so you don’t need to enter it each time
• Cheque: Include your reference on the back of the cheque to help HMRC match the payment correctly

When paying HMRC on time, use your 13-character AORN. If paying early or late, add the four digits to make a 17-character reference that tells HMRC which period you're covering.

The payment process

Follow these steps to make sure your payment is allocated correctly: 

• Check your payment deadline: PAYE payments are due by the 22nd of the following month when you pay electronically, or by the 19th when you pay by post
• Add the period digits if needed: If you're paying early or late, work out the four digits for that month or quarter and add them to your reference
• Enter the full reference: The complete reference links your payment to the correct PAYE account and payment period
• Keep a payment record: Save your bank confirmation showing the date, amount, and reference you used, so you can sort out any query with HMRC later

🧠 Good to know 

If you’re a small employer whose PAYE bill comes in under £1,500 a month, you can pay quarterly instead of monthly. Your AORN stays the same.

What happens if your business changes?

Your AORN is tied to your PAYE scheme, not you personally, which means business changes can affect it.

If you close one PAYE scheme and open a new one, whether because you've changed legal structure, gone through a merger, or restructured how your payroll runs, you'll be issued a new AORN for the new scheme. 

If you continue using the old one after the change, your payments will go to a scheme that's no longer active and won’t be properly matched.

Activities like hiring additional employees, changing your business address, or updating your bank details won’t affect your AORN. 

It stays fixed for as long as the underlying PAYE scheme remains open, so there's no need to check for updates unless HMRC specifically tells you your scheme has changed.

What happens if you lose your Accounts Office Reference Number?

If you've lost track of your AORN, check in these places before you contact HMRC:

• Your original HMRC registration letter: This is the letter HMRC sent when you first registered as an employer, and it lists both your Employer PAYE Reference and your AORN
• Your HMRC online business tax account: You can find your AORN by logging in and going to your PAYE for employers section – the reference is listed under your employer details alongside your other scheme information
• Your payroll software: If you've already run payroll once, the reference is almost certainly stored in your software's employer settings, since it's required to report payroll to HMRC and during initial setup
• Previous correspondence from HMRC: Reminder letters, penalty notices, and annual review letters about your PAYE scheme often repeat the reference somewhere in the text
• Your accountant or payroll bureau: If someone else manages your payroll on your behalf, they'll have the reference

If you’re still unable to find your AORN, you'll need to call HMRC's employer helpline. Be ready for a security check, as HMRC will often ask for business details such as your Employer PAYE Reference or company registration number before confirming the AORN over the phone.

What to do if you use the wrong Accounts Office Reference Number

If you use the wrong AORN, contact HMRC and ask them to trace and reallocate the payment. They will usually need details such as the payment date, amount, bank details, and the reference you used.

Keep a copy of your payment confirmation and any correspondence with HMRC until the issue is resolved.

ANNA: a simpler way to manage PAYE and payroll

Keeping track of PAYE deadlines, payment references, and payroll admin can take up significant time, which is precious when you’re running a small business. 

ANNA helps simplify your payroll process by keeping your PAYE information organised, automating routine tasks, and helping you stay on top of your tax deadlines.

Here’s what it allows you to do:

• Run payroll and manage PAYE payments from your ANNA business account, with key payment details stored and applied automatically
• File your Corporation Tax return, keep your company compliant, and meet HMRC deadlines easily
• Submit your Self Assessment tax return directly through ANNA for free if you're a sole trader or company director who needs to file one
• Create and send invoices while keeping your income records organised in one place
• Capture receipts and categorise expenses automatically 
• Set aside money with Smart Pots, so you’re prepared for PAYE, VAT, and other business payments
• Get real-time tax estimates and have a clear picture of what you need to pay
• Stay ahead of deadlines with smart reminders for important payroll, tax, and filing dates
• Access UK-based support 24/7 if you need help with your account or business admin

Open an ANNA account today and centralise your payroll, payments, and everyday business admin.