Business

What is Purchase Order vs Invoice?

Purchase order vs invoice — what's the difference? Learn when each document is used, who issues it, and how AP teams match them for accurate B2B billing and payment processing.

Purchase Order vs. Invoice: The Core Difference

The fundamental distinction between a purchase order (PO) and an invoice comes down to who issues it and when: - A purchase order is issued by the buyer — before the transaction occurs - An invoice is issued by the seller — after the transaction occurs Think of the PO as the buyer's purchase authorization and the invoice as the seller's payment request. In a formal B2B procurement workflow, these two documents bookend the transaction: the PO opens it, the invoice closes it.

Side-by-Side Comparison

| | Purchase Order (PO) | Invoice | |---|---|---| | Who issues it? | Buyer | Seller | | When is it issued? | Before the transaction | After goods/services are delivered | | What does it do? | Authorizes and commits to a purchase | Requests payment for goods/services delivered | | Who accepts it? | Seller | Buyer | | Creates obligation for | Buyer (to pay upon delivery) | Seller (to deliver goods/services) | | Contains | What's being bought, quantities, agreed prices | What was delivered, what is owed, payment terms | | Matched by AP? | Yes — used as the basis for invoice matching | Yes — matched against PO by buyer's AP team | | Required for transaction? | No — many transactions skip POs | Yes — required to formally request payment |

The Purchase Order Workflow

In a full-cycle PO-to-payment workflow, the sequence looks like this: 1. Buyer creates a PO — specifying what they want to buy, in what quantity, and at what price 2. Seller receives and accepts the PO — confirming the order or requesting changes 3. Goods or services are delivered — per the terms specified in the PO 4. Seller sends an invoice — referencing the PO number for easy matching 5. Buyer's AP team matches the invoice to the PO — verifying authorization and accuracy 6. Payment is issued — according to the payment terms on the invoice

When POs Are Required (and When They Aren't)

POs are typically required in: - Enterprise B2B transactions with formal procurement policies - Government contracts and public-sector purchasing - Large nonprofit or grant-funded purchases - Any buyer with a structured 3-way match process (PO → receipt → invoice) POs are often skipped in: - Freelance and consulting engagements without a formal procurement process - Small business transactions and retail sales - Professional services billed by time and materials - Any transaction where the seller initiates billing directly

Why Freelancers Should Always Reference PO Numbers

If a client sends you a PO, that number is your best friend in the billing process. Here's why: - Faster payment — AP teams process POs and invoices together; without the PO number, your invoice may sit in a queue waiting for manual matching - Reduced disputes — referencing the PO confirms the work was authorized and prevents scope disputes later - Professionalism — matching PO numbers signals that you understand enterprise procurement workflows and are a serious vendor

The Bottom Line

Purchase orders and invoices are two sides of the same transaction — but they belong to different parties and serve different purposes. As a freelancer or small business owner, understanding when each document appears in your workflow helps you manage billing, reduce payment delays, and communicate more professionally with enterprise clients. Key Takeaways: 1. A PO is the buyer's authorization; an invoice is the seller's payment request 2. POs always come before invoices in a formal procurement workflow 3. AP teams match invoices against POs — always include the PO number on your invoice 4. Many freelance transactions skip the PO entirely and go straight to invoicing 5. Eonebill lets you add PO numbers to every invoice for clean matching Send AP invoices that reference purchase orders and get paid faster — Try Eonebill Free View Pricing → | Glossary Home → | Home →

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Frequently Asked Questions

What is the main difference between a purchase order and an invoice?

A purchase order (PO) is issued by the BUYER before a transaction to authorize and commit to a purchase. An invoice is issued by the SELLER after delivery to request payment. The PO starts the process; the invoice closes it.

Which comes first, a purchase order or an invoice?

The purchase order always comes first. The buyer issues a PO to authorize the purchase. After goods or services are delivered, the seller issues an invoice requesting payment based on the authorized PO.

Can an invoice exist without a purchase order?

Yes. Many transactions — especially B2C sales, freelance work, and small business services — proceed without a PO. In those cases, the invoice is the first formal document in the transaction. A PO is not required for an invoice to be valid.

How do AP teams use purchase orders with invoices?

Accounts payable teams match incoming invoices against authorized POs to verify that purchases were pre-approved and goods or services were actually ordered. If an invoice doesn't match the PO, the AP team may reject it or place it on hold pending clarification.

Are both purchase orders and invoices legally binding?

Yes. Once a seller accepts a PO — by confirming the order or beginning delivery — it becomes a binding commitment. An invoice, once issued and accepted by the buyer, creates a legally enforceable debt for the amount stated.