Purchase Order vs Invoice: Key Differences

Short answer

A purchase order, or PO, is created by a buyer to authorize goods or services under stated quantities, prices, and terms. An invoice is created by the supplier to record the billable transaction and request payment. The PO comes before purchasing or delivery; the invoice follows the agreed billing event and should reference the PO when one exists.

Create the supplier's billing document with the free invoice generator, then match it to the customer's approved purchase order.

What is a purchase order?

A purchase order is a buyer-controlled procurement document. It can include:

• Buyer and supplier details.
• Unique PO number and issue date.
• Products or services authorized.
• Quantities, units, and agreed prices.
• Delivery location and requested date.
• Budget, project, department, or cost-center reference.
• Payment and purchasing terms.
• Approval status and authorized buyer.

The PO tells the supplier what the customer has approved. It does not prove that goods were delivered, services were completed, or payment was made.

What is an invoice?

An invoice is issued by the supplier and commonly includes:

• Supplier and customer billing details.
• Unique invoice number and invoice date.
• PO, contract, order, or project reference.
• Goods delivered or services supplied.
• Quantities, rates, discounts, fees, and line totals.
• Applicable tax, currency, total, and amount due.
• Due date and payment instructions.

Use the how to create an invoice guide for the complete field structure.

Key differences

• Issuer: The buyer issues the PO; the supplier issues the invoice.
• Purpose: The PO authorizes spending; the invoice requests payment.
• Timing: The PO comes before the purchase; the invoice follows the billable event.
• Numbering: PO and invoice numbers belong to different controlled systems.
• Status: A PO can be approved, open, partially fulfilled, or closed; an invoice can be sent, due, paid, overdue, or credited.
• Evidence: The PO supports authorization, while delivery and completion records support fulfillment.

Practical purchase example

A retailer sends PO-5018 to a wholesaler for 20 cases at $80 per case:

1. Authorized product value: 20 x $80 = $1,600.
2. The wholesaler delivers 18 cases and records 2 as backordered.
3. Invoice INV-2912 references PO-5018.
4. The invoice bills 18 cases at $80 = $1,440 before applicable tax and delivery charges.
5. A later shipment and invoice can cover the remaining 2 cases without rebilling the first 18.

The invoice should reflect actual billable fulfillment rather than blindly copying the original PO quantity.

PO number vs invoice number

The purchase order number identifies the buyer's authorization. The invoice number identifies the supplier's payment request. Put both on the invoice with clear labels.

Do not use a PO number as a substitute for a unique invoice number. See invoice number vs purchase order number for numbering examples.

Two-way and three-way matching

A two-way match compares the PO with the invoice. A three-way match also compares a receipt, delivery note, or service-completion record.

A reviewer can check:

• Correct buyer and supplier.
• Matching product or service descriptions.
• Authorized and delivered quantities.
• Agreed and invoiced prices.
• Delivery, freight, discount, and tax treatment.
• Valid references and approvals.

Differences should be investigated instead of automatically changing the invoice or PO.

What if the invoice exceeds the PO?

The difference may result from approved additional work, price changes, freight, tax, or an error. Obtain the required buyer approval or revised PO before expecting payment. Keep the change and authorization traceable.

Do not split or relabel a charge simply to bypass an approval limit. Follow the customer's procurement process.

Supporting documents

Useful records can include:

• Approved purchase order.
• Contract or quote.
• Delivery note or goods receipt.
• Timesheet or milestone acceptance.
• Approved change order.
• Expense evidence.

The invoice supporting documents guide explains how to attach only relevant and secure evidence.

Final checklist

• Buyer and supplier entities match.
• PO and invoice numbers are separately labeled.
• Invoice lines fit the authorized scope.
• Delivered quantities and completed services are verified.
• Prices, discounts, freight, and tax reconcile.
• Changes have appropriate approval.
• Currency and payment terms match the agreement.
• PO, fulfillment, invoice, and payment records remain linked.

Browse the blog archive for more procurement and invoice workflow guidance.

FAQs

Is a purchase order an invoice?

No. A PO authorizes a purchase; an invoice records the supplier's charge and requests payment.

Can an invoice be issued without a PO?

Yes, when the customer and transaction do not require one. If the buyer requires a PO, obtain the valid reference before invoicing to avoid approval delays.

Should the PO and invoice totals match?

They should reconcile according to the agreement and actual fulfillment. Partial deliveries, approved changes, freight, or tax can create explained differences.

Does a purchase order prove delivery?

No. It proves authorization. Use a delivery note, receipt, completion record, or other accepted evidence to confirm fulfillment.