Purchase Order vs. Invoice: What's the Difference?

A purchase order is created by the buyer to request goods or services from a supplier, while an invoice is created by the seller to request payment. The documents are related, but they occur at different points in the purchasing process and serve different purposes.

Purchase order vs. invoice at a glance

What is a purchase order?

A purchase order documents what the buyer intends to purchase. It commonly includes a PO number, supplier, delivery location, products, quantities, agreed prices, requested delivery date, and terms.

For inventory operations, the PO also provides visibility into stock that has been ordered but not yet received.

What is an invoice?

An invoice is a bill from the supplier. It typically identifies what the supplier says was provided, the amount due, taxes or other charges where applicable, payment terms, and payment instructions.

An invoice should not automatically be treated as proof that every ordered unit physically arrived.

Why businesses match purchase orders and invoices

Matching documents helps identify:

• Price differences
• Unexpected quantities
• Items billed but not ordered
• Short or partial deliveries
• Duplicate invoices
• Freight or other charges that differ from expectations

Two-way vs. three-way matching

Two-way matching commonly compares the purchase order with the supplier invoice.

Three-way matching adds receiving evidence, comparing what was ordered, what was physically received, and what was invoiced.

For inventory accuracy, the receiving step is especially important. If a PO says 100 units and the invoice bills 100 but only 94 arrive, inventory should reflect the 94 actually received while the discrepancy is resolved.

Example purchasing workflow

1. Inventory reaches a replenishment threshold.
2. The buyer creates a PO for the supplier.
3. The supplier confirms and ships the order.
4. The receiving team counts what arrived.
5. Inventory is updated from the received quantity.
6. The supplier invoice is checked against the PO and receipt.
7. Differences are resolved before payment according to company policy.

How POs connect to inventory replenishment

A good inventory replenishment process considers current stock, demand, supplier lead time, safety stock, and inventory already on order before creating another PO.

That prevents a low on-hand number from triggering duplicate purchasing when sufficient stock is already inbound.

Purchase order vs. sales order

A purchase order comes from the buyer. A sales order is typically the seller's internal or customer-facing record confirming a sale. The same transaction can therefore create different documents on each side.

Common purchasing-control mistakes

• Paying invoices without checking what was received
• Updating inventory from the PO quantity instead of receipt quantity
• Using email threads instead of consistent PO numbers
• Failing to record partial deliveries
• Creating duplicate POs because inbound stock is not visible

How Stash fits

Stash connects inventory, suppliers, purchase orders, forecasting, and multi-location stock. That gives operators a clearer purchasing record before inventory arrives and during receiving.

Frequently asked questions

Is a purchase order a bill?

No. A PO documents the buyer's order. The supplier's invoice is the document that requests payment.

Can an invoice exist without a purchase order?

Yes. Some businesses allow purchases without POs, although using purchase orders can improve purchasing control and reconciliation.

Should inventory be updated from the PO or the delivery?

Inventory should reflect what is actually received according to the business's receiving process, not simply the quantity originally ordered.