October 14, 2026 · EN · All articles

What Is a Purchase Order? (And How Small Businesses Use Them)

What is a purchase order?

A purchase order (PO) is a document a buyer sends to a supplier to order goods or services. It lists what you are buying, quantities, agreed prices, delivery terms, and payment terms — and it carries a unique PO number. Once the supplier accepts it, the PO becomes a legally binding contract: they commit to delivering exactly what the PO describes, and you commit to paying exactly the agreed price.

Think of it this way: when a supplier invoices you, that paper protects them. When you send a purchase order, the paper protects you.

How the PO process works in practice

1. You create the PO — items, quantities, unit prices, discount, tax, delivery date, and your PO number. Internal approval first if spending rules require it.
2. You send it to the supplier — email or portal. They confirm availability and accept (or negotiate).
3. They deliver — ideally referencing your PO number on the delivery note.
4. You check the delivery against the PO (right items, right quantities) — this is "receiving".
5. Their invoice arrives and you match it against the PO and the delivery before paying. Prices and quantities agree → you pay with confidence. They don't → you have the paper to dispute.

That three-point match — PO, delivery, invoice — is the core of professional purchasing. It takes seconds per order and closes the door on most supplier disputes.

Purchase order vs invoice: the key differences

• Who issues it: the buyer issues the PO; the seller issues the invoice.
• When: the PO comes before delivery; the invoice comes after.
• Purpose: the PO states what you ordered and agreed to pay; the invoice demands payment for what was delivered.
• Legal weight: an accepted PO is a binding purchase contract; an invoice is a payment demand backed by that contract.

Selling? You receive POs and issue invoices. Buying? You issue POs and receive invoices. A small business constantly does both — which is why mixing the two documents up causes accounting confusion.

Why bother with POs when you're small?

• Budget control. Nothing gets purchased without a document that shows who approved it and against what budget. No surprise invoices at month-end.
• Dispute protection. When a supplier bills $1,200 for what you ordered at $1,000, the PO settles it in one email.
• Cash-flow visibility. Open POs are committed spend. Seeing them lets you plan payments instead of reacting.
• Better supplier terms. Regular, documented order patterns are leverage when you negotiate prices or payment terms.
• Cleaner accounting. Expenses get matched to orders at receipt time, not discovered at invoice time — your books stay accurate.

Common purchase order mistakes

• No unique PO numbers — "that order from last month" is not an audit trail. Sequential numbering (like BC-2026-0001) keeps every order findable.
• Verbal orders followed by "confirming" POs — if it started as a phone call, the PO is a formality, not a control. Put the order in the PO.
• Prices that drift from the quote — if you negotiated $45/unit, the PO must say $45/unit, or the match step fails silently.
• No approval path — one person creating and approving their own POs defeats the purpose. Even in a 2-person business, a second set of eyes on spend over a threshold is worth it.
• POs that don't reach the bookkeeper — the invoice arrives, no one knows a PO exists, payment gets delayed and discounts lost.
• Skipping the receiving step — paying the invoice because "the PO says so" without checking the delivery actually happened.

What a good PO contains

• Unique PO number and issue date
• Your company details (name, address, contact)
• Supplier details
• Line items: description, quantity, unit price, per-line discount
• Discount and tax (VAT/sales tax) computed clearly
• Delivery address and expected date
• Payment terms (e.g. Net 30) and payment record
• Status tracking: draft → issued → partially paid → paid (or cancelled)

Managing POs without drowning in paper

At a few orders per month, Word templates and email work — badly, but they work. As volume grows, the failure modes appear fast: duplicate numbers, lost approvals, invoices paid twice, and no view of committed spend. Altera's Purchase Orders module keeps the whole chain in one place: POs with line items, discount and tax, supplier payments, automatic statuses (draft, issued, paid, cancelled), automatic numbering, downloadable PDF purchase orders, and a one-click PO button inside each supplier's record. It lives in the same system as your invoices, clients, and inventory — create a free Altera account and issue your first PO in minutes.

FAQ

Is a purchase order legally binding?

Yes — once the supplier accepts it (explicitly or by shipping), it functions as a contract. That is exactly why you want its terms to be accurate.

Do I need a PO for every small purchase?

Set a threshold. Many businesses require POs for anything above a set amount (e.g. $100–500) and let routine small expenses flow through with receipts. The point is control over meaningful spend, not bureaucracy over coffee.

What does "3-way match" mean?

Matching three documents before paying: the purchase order (what you ordered), the delivery note (what arrived), and the invoice (what they billed). All three agree → pay. Any mismatch → investigate first.

Can a purchase order replace a contract?

For straightforward, repeat purchases, yes — an accepted PO with clear terms is generally sufficient. For large, custom, or long-term engagements, a full contract plus POs is the safer structure.