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Key takeaways
- A purchase order is the buyer's written order. An invoice is the seller's request for payment.
- The PO comes first and authorises the spend. The invoice comes after delivery and triggers payment.
- Accounts payable matches the invoice to the PO, and often to the goods receipt, before it pays.
- A missing PO number is the commonest reason an invoice is rejected.
Free PDF and Excel: PO to invoice matching checklist. Get it below
The difference
A purchase order is a document a buyer sends to a seller to order goods or services. An invoice is a document the seller sends to the buyer to request payment for what was supplied.
The first is a promise to pay under stated terms. The second is the claim for that payment. A purchase order guide is already on the site: purchase order guide. This page looks only at how the two relate.
A buyer issues PO 5521 for 200 office chairs at 64.00 each, a total of 12,800. The supplier delivers 200 and invoices 12,800 citing PO 5521. AP matches the invoice to the PO and the receiving record, and pays on the due date.
If the invoice had said 210 chairs at 64.00, the match would fail and the invoice would be held until the supplier explained the 10 extra chairs.
Side by side
| Point | Purchase order | Invoice |
|---|---|---|
| Issued by | Buyer | Seller |
| When | Before delivery | After delivery |
| Purpose | Authorise and order | Request payment |
| Binding on | Buyer, once accepted by seller | Buyer, subject to match and approval |
| Contains | Items, quantities, agreed price, delivery and terms | Items delivered, prices, tax, due date, PO reference |
| Used by | Procurement, supplier | Accounts payable, tax |
Free PDF and Excel
PO to invoice matching checklist
A matching sheet that compares the PO, goods receipt and invoice, and a list of reasons matches fail.
- Matching sheet
- Reasons matches fail
- Query wording
- Excel matcher that flags price and quantity differences
How finance matches them
- The invoice arrives with the PO number.
- AP finds the PO and compares items, quantities and prices.
- For goods, AP checks the receiving record too. This is a three-way match.
- Differences are queried with the supplier or the requester.
- If everything agrees, the invoice is approved for the next payment run.
The full approval process is in the invoice approval and GRN guide. The seller's side of the order is the sales order. Where the invoice arrives before a PO exists, see check request form.
Why matches fail
- No PO number on the invoice.
- Price on the invoice differs from the PO.
- Quantity billed is more than received.
- Taxes or freight not on the PO.
- PO closed or expired before delivery.
- Invoice cites a valid PO.
- Items, quantities and prices agree.
- Goods or services were received.
- Tax and freight are as expected.
- Approver has signed.
- Payment terms match.
Last checked: 19 October 2026. General accounts payable practice.
Frequently asked questions
What is the difference between a purchase order and an invoice?
A purchase order is the buyer's order. An invoice is the seller's bill. The order comes first and the invoice follows delivery.
Does an invoice need a PO number?
If the buyer uses purchase orders, yes. Many reject invoices without one.
What is a three-way match?
A check that the purchase order, the goods receipt and the invoice agree before payment.
Can I pay an invoice with no PO?
Some companies allow it for approved categories. Others reject it. A check request may be used instead.
Who issues a purchase order?
The buyer, normally procurement or the requester through a system.