What Is a P.O. Number on an Invoice?
A P.O. number (Purchase Order number) on an invoice is a reference code from your client. Learn what a P.O. number means, why clients ask for it, how to add it correctly, and why it helps you get paid faster.
You finish a job, create a nice invoice, and send it to the client. A few hours later, they reply:
“Please add our P.O. number to the invoice before we can process payment.”
Many freelancers and small business owners see this message and think:
“What is a P.O. number? Why do they need it on my invoice? And where do I even put it?”
This short guide explains everything in simple terms:
What “P.O. number” actually means
Why do clients ask you to include it
When you really need to add one
Where to place it on the invoice
How to add it quickly using GenerateInvoice.net
What Does “P.O.” Stand For?
P.O. stands for Purchase Order.
A purchase order is an official document that your client creates and sends to you when they officially approve buying your product or service.
The P.O. number is simply the unique reference code printed on the purchase order (e.g., PO-45678, 2025-PO-123, REQ-9876).
Think of it as their internal tracking label — like a ticket number they use to follow the purchase through their system.
What Is a P.O. Number on an Invoice?
When a client asks you to include their P.O. number on your invoice, they want you to write it somewhere visible on the document you send them.
Example:
The client sends you PO #PO-56789
You add “P.O. #PO-56789” on your invoice
Now their accounts payable team can quickly find the matching Purchase Order in their system and approve your payment faster
Without the P.O. number, their team has to search manually or match by amount/date/client name — which takes longer and sometimes causes delays or lost invoices.
Why Do Clients Ask for a P.O. Number?
Most often this happens with:
Larger companies
Corporations
Government or public sector clients
Businesses that use formal purchasing systems
Their reasons:
Internal approval process — They cannot pay without linking your invoice to an approved P.O.
Budget tracking — The P.O. number ties the expense to a specific budget code
Prevent duplicate payments — Makes sure they don’t pay twice for the same job
Faster processing — Accounts payable teams can find and approve your invoice in seconds instead of hours or days
Audit trail — Creates a clear chain: Purchase Order → Your Invoice → Payment
Small individual clients, one-off retail customers, or very small businesses rarely use or need P.O. numbers.
When Do You Need to Include a P.O. Number?
Yes — when the client specifically gives you one (they will usually email it or write it on their Purchase Order document)
No — when the client never mentions a P.O. number, or says “no P.O. needed”
Best practice:
Early in the conversation (after they accept your quote), always ask:
“Do you have a purchase order number for this project? I’ll add it to the invoice, so your team can process payment smoothly.”
If they provide one, include it.
If not, no need.
Where Should You Put the P.O. Number on the Invoice?
Make it easy for the client’s accounts team to find:
Best spots (in order of preference):
In a dedicated “Reference” or “P.O. Number” field (many invoice tools have this near the top or under client details)
In the invoice header (example: “Reference: P.O. #PO-56789”)
In the notes/comments section at the bottom (still visible, but less prominent)
How it should look: Clear and short: “P.O. #PO-56789” or “Purchase Order: 2025-PO-123” Put it where it stands out but doesn’t clutter the design
How to Add a P.O. Number Using GenerateInvoice.net
It takes seconds and is completely free.
Choose any template
Fill in your details and the client's info
Add your line items as usual
Scroll to the Notes or Reference section (or custom text area)
Type: “P.O. Number: PO-56789” (or whatever they gave you)
Preview → the P.O. number appears clearly on the invoice
Download PDF or copy shareable link → send
The client sees it right away, their team matches it to their system instantly, and payment usually comes much faster.
Quick Summary
P.O. number = the client’s Purchase Order reference code
You add their P.O. number to your invoice
Purpose: Helps their accounts team find and approve your invoice quickly
When to include it: Only when the client gives you one
Where to put it: In the reference/notes field or header—make it visible
How to do it fast: Use GenerateInvoice.net → type it in notes → download/send
Adding the P.O. number is a small detail that can make a big difference—especially with corporate or larger clients.
Need to add one right now?
Go to https://generateinvoice.net — create your invoice, paste the P.O. number in the notes/reference area, and download PDF or share link instantly. Free, no signup required.