What is Purchase Order?
A purchase order (PO) is a commercial document issued by a buyer to authorize a purchase before payment. Learn the difference between a PO and an invoice, when freelancers need them, and how to use them in your billing workflow.
What Is a Purchase Order?
A purchase order (PO) is a formal commercial document a buyer sends to a vendor or service provider to authorize and initiate a purchase. It documents the buyer's intent to purchase specific goods or services at agreed-upon prices — creating a legally binding commitment once the seller accepts it. Think of it this way: the PO is the buyer's side of the transaction. While the seller sends invoices to request payment, the buyer sends POs to authorize purchases in advance. For freelancers, receiving a PO from a client signals that the engagement has passed internal approval — which significantly reduces the risk of non-payment.
Purchase Order vs. Invoice — Key Differences
| | Purchase Order (PO) | Invoice | |---|---|---| | Who issues it | Buyer | Seller | | When it's issued | Before the transaction | After goods/services are delivered | | Purpose | Authorizes and commits to a purchase | Requests payment for goods/services delivered | | Legal effect | Creates buyer's obligation to pay | Confirms seller's right to payment | | Binding? | Yes — once seller accepts | Yes — after acceptance of goods/services | | Matched by AP | Used by buyer's AP to match against invoice | Sent by seller to buyer's AP department |
Sample Purchase Order
PURCHASE ORDER TechCorp Inc — Procurement Department PO Number TCPO-2026-0193 PO Date March 10, 2026 Payment Terms Net-45 Delivery Date April 15, 2026 Issued By (Buyer): TechCorp Inc Accounts Payable Department 1 Infinite Loop, MS-AQ Cupertino, CA 95014 Issued To (Seller): Apex Consulting Group 840 Broadway, Suite 1200 New York, NY 10003 Description Qty Unit Price Total Q1 2026 Strategy Advisory — Monthly Retainer 1 $3,500.00 $3,500.00 Operations Audit — Phase 1 Report 1 $1,200.00 $1,200.00 Executive Workshop Facilitation 4 hrs $175.00 $700.00 Subtotal$5,400.00 PO Total$5,400.00 Terms & Conditions 1. Seller shall reference PO TCPO-2026-0193 on all invoices submitted. 2. Payment terms: Net-45 from date of invoice receipt. This PO is valid through April 15, 2026.
When Do Freelancers Encounter Purchase Orders?
POs are most common in formal B2B environments — corporate clients, government agencies, nonprofits, and any buyer with a structured procurement process. You won't see POs from small businesses or direct consumers, but they're nearly universal in enterprise freelancing. Typical scenarios for freelancers: - A mid-size tech company hires you for a 3-month project; their procurement policy requires a PO before any contractor can be paid - A nonprofit receives a grant and uses grant funds to hire a consultant — a PO is issued to authorize spending against the grant budget - A government agency contracts freelance services; the PO is part of a formal federal/state procurement process
How POs Flow Through Your Invoicing Workflow
When you receive a PO from a client, here's how it fits into your billing workflow: 1. Receive the PO — before starting any work, you have written authorization and an agreed budget 2. Review and accept — confirm the scope and total amount; note any constraints (e.g., not to exceed $X) 3. Deliver the work — execute against the scope as defined in the PO 4. Send your invoice — always include the PO number in the invoice header so the client's AP team can match it 5. Wait for payment — with a PO in hand, payment is far more predictable than with a verbal agreement
POs vs. Contracts — What's the Difference?
A purchase order covers a specific transaction: what is being bought, at what price, with what terms. A contract establishes the broader legal relationship: scope of work, IP ownership, confidentiality, termination clauses, and more. In practice, many freelance engagements have both: - A master services agreement (MSA) or contract that governs the overall relationship - Individual POs that authorize and budget specific engagements under that umbrella
The Bottom Line
Purchase orders are a sign of a mature, professional client — and a protection for you as a freelancer. When a PO lands in your inbox, you have written evidence that the work is authorized and funded. Always reference the PO number on your invoice to ensure smooth, fast payment. Key Takeaways: 1. A PO is the buyer's authorization to purchase — before delivery, before invoicing 2. Always reference the PO number on your invoice to ensure AP matching 3. Receiving a PO signals that the buyer's internal procurement has approved the engagement 4. For high-value or long-term freelance work, POs should accompany a broader contract 5. Eonebill makes it easy to reference PO numbers on every invoice you send Track purchase orders, send professional invoices, and get paid faster — Try Eonebill Free Ready to automate your invoicing workflow? Get started with Eonebill today. View Pricing → | Glossary Home → | Home →