A purchase order number is the buyer's reference that links an invoice to an approved order, budget and receiving record.
Place the exact PO number in a dedicated reference field and repeat it only where the buyer's submission rules require it.
Where the PO number goes on an invoice
Put the PO number on an invoice in a dedicated buyer-reference field near the invoice number and dates. Do not replace your invoice number with the purchase order number: they belong to different number systems and identify different documents. Repeat the PO number in an electronic submission field only when the customer’s procurement process requires it.
| Reference | Created by | Identifies | Example |
|---|---|---|---|
| Purchase order number | Buyer | The approved order | PO-2027-00842 |
| Invoice number | Seller | The issued invoice | IC-2027-0146 |
| Supplier or vendor number | Buyer | The seller in the buyer’s system | V-10492 |
| Receipt reference | Buyer | Goods or services accepted | GRN-6631 |
Three-way matching compares the purchase order, receipt, and invoice. If the quantity, price, tax, supplier, or reference differs beyond policy tolerance, the buyer routes the discrepancy for review. Using the PO number accurately can accelerate matching, but it does not prove that the goods arrived or that the invoice amount is correct.
How do you know the PO number? Ask the buyer’s authorized contact before billing and copy the exact identifier from the approved purchase order. Never invent a sequential number that looks like a buyer PO, and do not reuse a PO for work outside its scope.
Resolve a missing PO before submission
Ask the buyer who owns the purchase order and whether separate lines need separate references. An invoice number identifies your document; a PO number identifies the buyer order. Do not invent a PO number to fill a required field. If the buyer authorizes work without a PO, obtain its documented exception process before the invoice reaches accounts payable.
Example
The buyer issues PO-7842 for design services, and the seller includes PO-7842 on every related milestone invoice so accounts payable can match it.
What to watch for
Your own invoice number is not the buyer's PO number, and inventing a reference to bypass an approval requirement can lead to rejection.
Put the next step into practice
Read our guide to purchase orders, invoices and bills for the related workflow. Explore Invoice Crowd invoicing to see the product capabilities relevant to your setup.
