Invoice vs Purchase Order — Key Differences and When to Use Each

Invoices and Purchase Orders are both critical business documents — but they serve completely opposite purposes. Understanding the difference protects your business.

The Simple Explanation

Purchase Order (PO): Created by the BUYER and sent to the SELLER before goods are delivered. It says "I authorize you to sell me these items at this price."

Invoice: Created by the SELLER and sent to the BUYER after goods are delivered. It says "You owe me this amount for what I delivered."

A Typical Business Transaction Flow

1. Buyer creates a Purchase Order → sends to supplier
2. Supplier accepts the PO → begins production or prepares goods
3. Supplier delivers goods/services
4. Supplier creates Invoice → references the PO number
5. Buyer receives Invoice → matches it against the PO
6. Buyer approves and pays

When to Use a Purchase Order

• When ordering goods from a supplier or vendor
• When you need a formal authorization trail for accounting
• For large orders where price must be locked in advance
• When ordering from a new supplier for the first time
• For government or corporate procurement

When to Use an Invoice

• After delivering goods or completing a service
• As a freelancer billing a client
• When requesting payment for any work done
• For recurring monthly billing
• As the legal document requesting payment

Small Businesses — Do You Need Both?

If you are a freelancer or small service business, you typically only need invoices. Purchase orders are more common in product-based businesses, retail, manufacturing and corporate environments. However, even freelancers benefit from using POs when engaging with corporate clients — it protects you with a formal authorization.

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