Daily Junction.mobi portalBusiness · February 19, 2025 · Marcus Vale · 6 min
A purchase order is a buyer's formal request to buy goods or services at agreed terms. Here is what a PO contains, how it differs from an invoice, and why small businesses use them.
A purchase order is a document a buyer sends to a supplier to confirm exactly what they want to buy, in what quantity, and at what agreed price. In one sentence: it is the formal way a business says "yes, we want this, on these terms" before any goods or services change hands. Familiar to anyone who has worked in procurement, the humble purchase order — usually shortened to "PO" — is one of those unglamorous tools that quietly keeps a business's spending under control.
Many small business owners get by without them for years, ordering on the phone or by email and sorting out the details later. That works until it doesn't — until a supplier delivers the wrong quantity, charges more than expected, or a bill arrives that nobody can quite remember authorising. A simple purchase order system prevents exactly these headaches. This guide explains what a purchase order is, what it contains, how it differs from an invoice, and when it is worth using.
A purchase order is a commercial document issued by a buyer to a supplier, setting out the details of an intended purchase. It is created and sent before the goods or services are delivered, and it records the buyer's offer to buy on specific terms.
The key thing to understand is the direction of travel. A purchase order flows from the buyer to the seller, and it comes first in the transaction. That single fact is what distinguishes it from most of the other paperwork in a sale, and it is the source of most of its usefulness.
A clear PO leaves no room for ambiguity about what has been ordered. A typical one includes:
The PO number matters more than it looks. It lets both sides track the order from placement through delivery to payment, and it lets the buyer match an incoming invoice back to what was actually ordered. Suppliers often insist on it appearing on invoices precisely so payment can be processed without a hunt through records.
This is the comparison that trips people up most often, so it is worth being precise.
| Purchase order | Invoice | |
|---|---|---|
| Who creates it | The buyer | The supplier |
| When | Before delivery | After delivery |
| Purpose | To order goods or services | To request payment |
| Direction | Buyer to supplier | Supplier to buyer |
In plain terms: the purchase order opens the transaction by confirming what is being bought, and the invoice closes it by asking for the money. A well-run business matches the two — together with proof of delivery — before paying, a check often called "three-way matching" that catches errors and overcharging. Keeping these documents straight is a core part of bookkeeping, and good accounting software will link a PO to its invoice automatically.
On its own, a purchase order is an offer to buy. It becomes a legally binding contract once the supplier accepts it — by confirming the order, or simply by fulfilling it. At that point both sides are bound by the terms the PO records: the items, quantities, prices and conditions.
This is much of the point of using POs at all. By writing down what was agreed before delivery, a purchase order gives both buyer and supplier a clear record to rely on if something goes wrong. If the supplier delivers the wrong amount or tries to charge a higher price, the PO is the evidence of what was actually agreed. It works hand in hand with your wider terms and conditions, which set the background rules for how you trade.
Beyond creating a binding record, POs deliver several practical benefits.
Spending control. Requiring a PO before anything is ordered means purchases are authorised in advance, not discovered after the money is spent. For businesses where several people can buy things, this prevents budgets from quietly leaking.
A clear audit trail. Every purchase has a documented origin, which makes record-keeping, VAT and year-end accounts far simpler. HMRC expects you to keep proper records, and POs feed naturally into that.
Fewer disputes. With price, quantity and delivery agreed in writing up front, there is far less to argue about later.
Better cash flow planning. Outstanding POs show what you have committed to spend, helping you forecast outgoings. Pair that with good cash flow management and you get a much clearer picture of where the money is going.
Smoother supplier relationships. Clear orders are easier for suppliers to fulfil accurately, which builds trust over time.
Purchase orders are not legally required, and for a one-person business buying the odd thing online they may be more trouble than they are worth. The point at which they start to pay off is usually when one or more of these is true:
You do not need an expensive system to start. A simple numbered template, or the purchase order function built into most accounting software, is enough. The discipline matters more than the tool: agree before you buy, record what you agreed, and match it against what arrives and what you are billed.
If you want to introduce POs without overcomplicating things:
Within a few weeks this becomes second nature, and you will wonder how you tracked spending without it.
A purchase order is a buyer's formal request to buy goods or services at agreed terms, sent to a supplier before anything is delivered. Once accepted, it generally becomes a binding contract, giving both sides a clear record of what was agreed on price, quantity and delivery. It differs from an invoice, which the supplier sends afterwards to request payment — the PO opens the transaction, the invoice closes it. For small businesses, POs bring control over spending, a clean audit trail, fewer disputes and better cash flow visibility. You do not need them for every purchase, but once you buy regularly or in larger amounts, a simple purchase order system is well worth the small effort it takes to run.
![[View image]](/img/what-is-a-purchase-order.jpg){kind=link}