A purchase order is an official document that a buyer sends to a seller to confirm the intent to purchase specific goods or services at an agreed-upon price. It spells out what is being ordered, how much it costs, and the terms of the deal. For the self-employed, a purchase order, often abbreviated as PO, is the document a larger client may issue before you start work, confirming they have approved the spend.
We spent several hours reviewing procurement guidance, accounting resources, and the billing practices of agencies and corporate clients to compile this guide. We focused on what an independent contractor needs to know when a client introduces a PO into the relationship.
In this article, we will define a purchase order, explain what it includes, compare it to an invoice, and show how it fits into the payment process.
What Information Does a Purchase Order Include?
A purchase order carries the key details of a planned transaction. It records the buyer and seller, a unique PO number, and a clear description of the goods or services. It also lists quantities, agreed prices, and the expected delivery or completion date.
Just as important, a PO states payment terms, such as net 30. Because the buyer creates the document, it reflects their internal approval to spend. That approval is exactly what makes a PO valuable to you as a contractor.
How Is a Purchase Order Different From an Invoice?
The two documents look similar, yet they flow in opposite directions. A purchase order is issued by the buyer at the start of a deal. An invoice is issued by the seller after the work is done or the goods are delivered.
Think of it as a matched pair. The PO says we agree to buy this, and the invoice later says Here is the bill for what you ordered. When you reference the PO number on your invoice, you help the client’s accounting team match the invoice to the PO and pay you faster.
Why the PO Number Matters on Your Invoice
Larger companies often refuse to pay an invoice that lacks a valid PO number. Their systems link payments to approved purchase orders, so a missing number can stall your money for weeks. Always ask for the PO before you begin, then quote it on every invoice.
One freelance marketer learned this the hard way. She delivered a $7,000 project, invoiced without a PO number, and waited nine weeks while the client’s finance team hunted for approval. A PO referenced upfront would have prevented the entire delay.
When Will You Encounter a Purchase Order?
Most solo clients and small businesses skip purchase orders entirely. You are most likely to meet a PO when you work with mid-sized or large organizations, government agencies, or universities. These clients use procurement systems that require a PO for any outside spend.
If a client mentions raising a PO, treat it as a good sign. It means the budget is approved and the money is set aside. In that sense, a purchase order can give you more security than a casual email agreement.
How Does the Purchase Order Process Work?
The process usually follows a clear sequence. First, you and the client agree on scope and price, often through a proposal or quote. Next, the client issues a purchase order with a unique number that authorizes the spend.
You then complete the work as described on the PO. Finally, you send an invoice that references the PO number, and the client’s system matches the two before releasing payment. Each step creates a paper trail that protects both sides.
What if the scope changes midway?
Scope creep is common, and a PO handles it cleanly. If the client asks for extra work beyond the original order, request a revised or additional purchase order before you proceed. Doing so ensures the new work is approved and that you will actually be paid for it.
Skipping that step is risky. Without an updated PO, the extra hours may fall outside the approved budget, leaving you to argue for payment after the fact. A quick request upfront avoids that uncomfortable conversation.
Do You Need to Issue Purchase Orders?
As a one-person business, you rarely need to issue POs yourself. You will more often receive them. That said, if you regularly buy from subcontractors or suppliers, sending your own purchase orders can bring order to your spending and create a record of what you approved.
For most freelancers, though, the priority is understanding the POs clients send you. Knowing how to read one, reference it, and request changes keeps your payments on schedule.
Do This Week
To get comfortable with purchase orders, work through these steps over the next seven days:
- Ask new corporate clients whether they use POs
- Request a PO number before starting approved work
- Add a PO number field to your invoice template
- File each PO alongside its matching invoice
- Confirm the payment terms listed on every PO
- Request a revised PO whenever the scope expands
- Review past late payments for missing PO numbers
- Create a simple PO template if you buy from suppliers
Final Thoughts
A purchase order is not red tape. It is a signal that a client has approved the budget and committed to paying you. Once you understand how a PO works, you can use it to protect your time and speed up your payments.
Ask about purchase orders early in any corporate engagement, then reference the PO number on every invoice. That small habit removes one of the most common reasons freelancer payments get stuck.
Photo by Rupixen: Unsplash
