Glossary
What is a PO number?
A PO number is the reference code a buyer assigns to a purchase order. Learn why it belongs on your invoice and what to do when a client has none.
Updated · By PayToMe Editorial
A PO number is the unique reference code a buyer assigns to a purchase order. When you invoice that buyer, you quote the same number so their team can match your invoice to the order they approved.
How it works
The buyer creates a purchase order before work starts, and the system assigns it a number, such as PO-2026-1187. Formats vary by company. The number follows the order through delivery and billing.
On your side, the process is short:
- Ask for the PO number when you accept the job, and confirm the scope and price it covers.
- Put it on the invoice in a clearly labeled field.
- Match the amounts. Line items and totals should agree with the order, or you should explain the difference.
- Send the invoice to the address the client’s accounts payable team uses.
Many larger companies will not pay an invoice that has no PO number, or one that does not match the order. The invoice can be rejected or sent back, which delays payment. Missing PO numbers are one of the most common avoidable reasons for slow payment.
If the work grows beyond the original order, ask for a revised PO or a new one before invoicing extra. Do not squeeze extra work under the old number.
Example
A client issues PO-2026-1187 for $3,600. You deliver and invoice.
| Field | Value |
|---|---|
| Invoice number | INV-0231 |
| PO number | PO-2026-1187 |
| Line 1: Site survey, 8 hr x $150 | $1,200.00 |
| Line 2: Report, 1 x $2,400 | $2,400.00 |
| Total | $3,600.00 |
The total equals the approved order, so the match is simple. If you add a $400 extra, ask for a PO change first. Add a PO field to your invoice with the free invoice generator, and check that each line item agrees with the order.
Related terms
- Purchase order: the document the number belongs to.
- Accounts payable: the team that pays your invoice.
- Line item: the rows that should match the order.