InvoiceTools
LoginSign Up

Home/Glossary/PO number

PO number

A PO number (purchase order number) is the client's own reference for an order, quoted on your invoice so their accounts team can match it to the purchase order they approved.

Example

"Your PO: 4520" beside "Invoice: INV-2026-0041".

Also called a purchase order number, a customer PO, or an order reference.

Make a purchase order free

What it means in practice

Larger clients raise a purchase order before work starts and will not pay an invoice that does not carry its number. It is the single most common reason an invoice sits in someone's system untouched.

Ask for the PO number when the job is agreed, not when the invoice bounces. Put it near your own invoice number, clearly labeled as theirs.

Covered in full in the guide to invoice numbers.

A purchase order followed from raising to paymentThe client raises PO 88-2291, the work is done, invoice INV-2026-0041 quotes the number, the two are matched at 1,299 and the invoice is paid.WHY THE INVOICE IS SITTING THEREHarbor Property Group raise PO 88-2291 before the work startsClientraises the POPO 88-2291Youdo the work14 Oak StreetInvoicequotes the POINV-2026-0041MatchedPO meets invoice1,299 = 1,299Paid14 October1,299.00No PO number on the invoiceIt never reaches the person who can approve it. Nobody rejects it and nobody tells you.
The purchase order comes first and the number travels with it. An invoice that arrives without it has nothing to be matched against.

Where it shows up on the paperwork

It goes at the top of your invoice next to your own invoice number, clearly labeled as theirs. Some clients also want it on the delivery note and the packing slip.

What goes wrong

  • Sending the invoice and asking for the PO number afterwards.
  • Putting their PO number where your invoice number should be, so neither system matches.
  • Guessing at a number rather than asking, which produces an invoice that will bounce quietly.

Common questions

What happens if I invoice without a PO number?

At a large client, usually nothing at all: the invoice sits unmatched until someone chases it. Ask for the number when the job is agreed, not when the invoice is late.

Is a PO number the same as an invoice number?

No. The PO number is the client's reference for the order they raised. The invoice number is yours for the bill you issued. Both appear on the invoice.

Two ways to send the document

Download it and send it yourself, and nothing is stored on our servers. Or send it as a link and stop wondering whether it arrived, was read, or is sitting in a queue because something is missing from it.

How invoice tracking worksBuild a document free

The first four documents you send as a tracked link are free with an account. Everything else on InvoiceTools.com stays free. Generators, calculators and downloads need no account; template designs need a free one.