Purchase Order vs Invoice: Key Differences
By Farasat Abbas Naqvi · Published June 15, 2026
A purchase order (PO) is a document the buyer sends to the seller to authorize a purchase; an invoice is the document the seller sends to the buyer to request payment once the goods or services are delivered. They are different ends of the same transaction, issued by different parties, and they must always reconcile.
Who issues what, and when
- Purchase order — created by the buyer, sent to the seller, before work or shipment begins.
- Invoice — created by the seller, sent to the buyer, after goods are delivered or services rendered.
Side-by-side comparison
| Aspect | Purchase Order | Invoice |
|---|---|---|
| Issued by | Buyer | Seller |
| Purpose | Authorize purchase | Request payment |
| Timing | Before delivery | After delivery |
| Numbering | PO-prefix sequence | INV-prefix sequence |
| Legally | Offer to buy | Demand for payment |
The three-way match
Mature accounts payable processes match the PO, the goods-received note, and the invoice before approving payment. Any mismatch (quantity, price, item) blocks the payment until resolved. Our PO workflow guide walks through approvals.
Worked example
Acme issues PO-0091 to a supplier for 50 units of a part at $20 each ($1,000 total). The supplier ships the parts and sends invoice INV-2034 referencing PO-0091, billing $1,000 plus tax. Accounts payable verifies the match and pays per the agreed Net 30 terms.
When you need each
- Always use a PO for repeat suppliers, large purchases, regulated procurement, or any spend that requires manager approval.
- Always issue an invoice when you deliver goods or services and want to be paid — every time, even if a PO was not raised.
Templates and tools
- Free purchase order template
- Free invoice templates
- Create a purchase order now — no signup required.
Frequently asked questions
Who issues the purchase order and who issues the invoice?
The buyer issues the purchase order to authorize a purchase. The seller issues the invoice after delivery to request payment.
Do you need a PO before an invoice?
Not always. POs are standard in B2B and procurement-driven workflows, but small purchases and many service engagements skip straight to the invoice.
Can a single document be both?
No. The PO and invoice are issued by different parties at different points in the transaction and must remain separate documents for audit and accounting.
Frequently Asked Questions
Who issues the purchase order and who issues the invoice?
The buyer issues the purchase order to authorize a purchase. The seller issues the invoice after delivery to request payment.
Do you need a PO before an invoice?
Not always. POs are standard in B2B and procurement-driven workflows, but small purchases and many service engagements skip straight to the invoice.
Can a single document be both?
No. The PO and invoice are issued by different parties at different points in the transaction and must remain separate documents for audit and accounting.