# What Is a Purchase Order?

> 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.

*Section: Business — By Marcus Vale (Editor-in-Chief & Business & Markets Editor) — Published February 19, 2025 — 6 min read*

Canonical URL: https://dailyjunction.co.uk/business/what-is-a-purchase-order
Tags: purchase order, procurement, small business, invoicing, bookkeeping

## Key takeaways

- A purchase order (PO) is a document a buyer sends to a supplier to confirm exactly what they want to buy, in what quantity, and at what price.
- Once a supplier accepts a PO, it generally becomes a binding contract, protecting both sides by recording the agreed terms.
- A purchase order is raised by the buyer before the goods arrive; an invoice is raised by the seller afterwards to request payment.
- POs improve control over spending, create an audit trail, and make it easier to match orders, deliveries and bills.
- Even small businesses benefit from a simple PO system once they buy regularly from suppliers.

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.

## What a purchase order is

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.

## What a purchase order contains

A clear PO leaves no room for ambiguity about what has been ordered. A typical one includes:

- A unique **PO number** for tracking and reference.
- The buyer's and supplier's names and contact details.
- A description of each item or service, with quantities.
- The agreed price per item and the total.
- Delivery details — where, when and how.
- Payment terms (for example, payment due 30 days after delivery).
- Any relevant terms and conditions.

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.

## Purchase order vs invoice

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](/business/how-to-do-bookkeeping), and good [accounting software](/business/choosing-accounting-software) will link a PO to its invoice automatically.

## Are purchase orders legally binding?

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](/business/how-to-write-terms-and-conditions), which set the background rules for how you trade.

## Why businesses use purchase orders

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](/business/cash-flow-management-small-business) 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.

## When a small business should start using them

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 buy regularly from the same suppliers.
- [ ] More than one person can place orders on the business's behalf.
- [ ] Individual purchases are large enough that an error would hurt.
- [ ] You have had disputes over what was ordered or what it should cost.
- [ ] You want tighter control over spending as the business grows.

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.

## A simple way to begin

If you want to introduce POs without overcomplicating things:

1. Create a basic PO template with a unique numbering system.
2. Decide a threshold above which a PO is required (small purchases can stay informal).
3. Send the PO to the supplier and keep a copy.
4. When goods arrive, check them against the PO.
5. When the invoice arrives, match it to the PO and the delivery before paying.

Within a few weeks this becomes second nature, and you will wonder how you tracked spending without it.

## The bottom line

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.

## Frequently asked questions

### Is a purchase order a legally binding contract?

On its own a purchase order is an offer to buy. Once the supplier accepts it — by confirming the order or fulfilling it — it generally becomes a legally binding contract on the terms it sets out. That is much of its value: it records what both sides agreed, reducing the scope for disputes later.

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

A purchase order is created by the buyer and sent to the supplier before the goods or services are delivered, to confirm what is being ordered. An invoice is created by the supplier and sent to the buyer afterwards, to request payment. The PO starts the transaction; the invoice closes it.

### Do small businesses need to use purchase orders?

They are not legally required, but they become valuable once you buy regularly or in larger amounts. POs control spending, prevent misunderstandings about price and quantity, and create a clear record that makes bookkeeping and dispute resolution easier. Very small or one-off purchases may not justify the effort.

### What is a PO number and why does it matter?

A PO number is a unique reference assigned to each purchase order. It lets both buyer and supplier track an order through delivery and payment, and lets the buyer match the invoice back to the original order. Suppliers often ask for it on invoices so payment can be processed quickly.

## Sources

- [GOV.UK — Invoicing and taking payment from customers](https://www.gov.uk/invoicing-and-taking-payment-from-customers)
- [GOV.UK — Keeping your pay and tax records](https://www.gov.uk/keeping-your-pay-tax-records)
- [British Business Bank — Finance hub](https://www.british-business-bank.co.uk/finance-hub)

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