Submitting an invoice can involve several pieces of information, and one detail you may be asked to provide is a purchase order (PO) number. While it may seem like a small addition, the PO number plays a significant role in ensuring your invoice is reviewed and approved without delays.
A PO number acts as a link between the institution’s internal purchase request and the invoice you submit, helping their finance team verify the charge and process payment efficiently.
So, what exactly is a PO number? Who is responsible for issuing it, and how do they benefit your invoicing process?
This article is written for authors and institutional administrators who are requesting or submitting invoices. It will therefore explain the purpose of PO numbers, why institutions rely on them, and how authors can use them correctly when preparing invoices. It also includes practical guidance to help you avoid common issues and ensure your invoice is processed efficiently.
In this article, we answer these questions:
- What do I need to know about purchase orders?
- What key information should each purchase order include?
- What is a PO number?
- Do I need a PO number?
- What is the importance of a PO number in business transactions?
- Who is responsible for providing the PO number?
- What is the difference between an invoice number and a purchase order number?
- How is a purchase order number generated?
- What are some common PO number formats?
- Tips for using PO numbers correctly on invoices
What do I need to know about purchase orders?
Before looking at PO numbers, it helps to understand what a purchase order is. A purchase order (PO) is a document the buyer sends to the seller to confirm what they want to purchase. It outlines the key details of the order - such as the items or services requested, the quantity, the agreed price, and when they should be delivered.
Once the seller accepts the purchase order, it becomes a formal agreement between both parties. This shared record helps ensure everyone is clear on what has been approved and what should be supplied.
Consistent use of purchase orders ensures a smoother and more efficient procurement process. They help avoid misunderstandings, reduce errors, and provide a clear reference point when it comes time to issue or review an invoice. In short, POs help keep transactions organised from start to finish.
What key information should each purchase order include?
For a purchase order to function effectively, it needs to contain all the key details that outline the agreement between the buyer and the seller. This helps avoid confusion later and ensures both parties have a shared understanding of what has been approved.
A well‑structured purchase order typically includes:
- Buyer and seller contact details
- A PO number to identify and track the order
- A description of the items or services, including quantities and prices
- Payment terms, such as due dates or accepted methods
- Delivery information, including the address and expected delivery date
- Any additional terms or conditions relevant to the order
These elements work together to create a clear, complete record of the transaction.
What is a PO number?
A PO number is a unique reference code assigned to a purchase order issued by the buyer. It helps both the buyer and the seller track the transaction throughout the procurement and payment process.
Organisations use PO numbers to match an invoice to the original order, confirm the agreed costs, and ensure the correct budget is being charged. This is why many institutions require the PO number to appear on the invoice before they can approve payment.
Do I need a PO number?
As previously mentioned, some institutions require a purchase order (PO) number before they can approve and pay an invoice.
If your institution uses PO numbers:
- You must request the PO number from your finance or procurement team
- You should provide the PO number when requesting or submitting the invoice
If your institution does not use PO numbers, you can usually proceed without one.
What is the importance of a PO number in business transactions?
PO numbers do far more than label a document. When used consistently, they provide a clear link between what was ordered and what is being billed.
Here are some of the key reasons PO numbers are important:
- Better tracking: A PO number makes it simple to locate and review a specific order, especially when dealing with large volumes of transactions.
- Fewer errors: Matching a purchase order to its corresponding invoice helps prevent issues such as duplicate payments, incorrect deliveries, or disputes over charges.
- Clear audit trails: PO numbers create a documented path from order to payment, supporting both internal checks and external audits.
- Improved communication: When both the buyer and seller refer to the same PO number, it reduces the chance of confusion or misaligned information.
In practice, the process starts when the buyer issues a purchase order for the goods or services they need. Once the seller fulfils the order, they send an invoice that should include the same PO number. This allows the buyer to quickly confirm that the invoice matches the original request.
Using PO numbers correctly helps streamline approvals, supports timely payments, and contributes to a smoother overall transaction for both parties.
Who is responsible for providing the PO number?
The PO number is always issued by the buyer - in this case, the institution or organisation paying the invoice fee. Authors do not create PO numbers themselves.
If your institution requires a PO number for payments, you will need to request it from your finance or procurement team before submitting your invoice. They will generate the purchase order and share the PO number with you.
What is the difference between an invoice number and a purchase order number?
Although PO numbers and invoice numbers may look similar, they serve different purposes in the purchasing and payment process.
- PO number: Created by the buyer, this number is used to track the purchase order throughout the procurement workflow.
- Invoice number: Issued by the seller, this number identifies the invoice itself and is used for billing, payment tracking, and maintaining accurate financial records.
Understanding the difference between these two identifiers helps ensure transactions are recorded correctly and reduces the chance of confusion during approval or payment.
How organisations create PO numbers
Organisations typically create PO numbers in one of two ways:
- Manual numbering: A team member assigns each new purchase order a number based on an internal format or sequence.
- Automated numbering: Financial or procurement software generates PO numbers automatically according to predefined rules.
The method an organisation chooses usually depends on its size, the volume of transactions it handles, and how structured its internal processes are. This means authors may see PO numbers in different formats depending on the institution, but the purpose remains the same: to identify and track the purchase order.
What are some common PO number formats?
PO numbers vary depending on the organisation’s internal system. Some examples include:
- Sequential numbers: PO‑001, PO‑002
- Date-based formats: 2026/PO‑001
- Department-based codes: PO‑PUB‑001 (e.g., for the publishing department)
- Project-based codes: PO‑PROJ1‑123
You do not need to interpret or modify the PO number - simply copy it exactly as provided.
Tips for using PO numbers correctly for invoices
When requesting or submitting an invoice:
- Confirm whether your institution requires a PO number for the relevant payment
- Request the PO number before submitting your invoice request
- Enter the PO number exactly as provided - do not edit, abbreviate, or reuse a PO number
- Ensure the PO number matches the purchase order issued by your institution
- Keep a record of the PO number for reference if payment questions arise
Invoice processing may be delayed if:
- A required PO number is missing
- The PO number on the invoice does not match the institution’s purchase order
- An incorrect or outdated PO number is used
Checking these details before submitting your invoice helps avoid delays.
Summary
The above article helps to explain how purchase orders and PO numbers are used in payment processes, including what they are, who issues them, and why some institutions require them. By outlining both the purpose of PO numbers and how they fit into institutional approval processes, this guidance is intended to give authors the context they need to understand requests for PO numbers and to provide them correctly when submitting or requesting an invoice.