Purchase Order vs Purchase Invoice: Controlling What You Spend

Most businesses put real effort into the documents they send customers and very little into the documents they receive from suppliers. That asymmetry is expensive, because the buy side is where money leaves without anyone approving it.

What each one is

• A purchase order (PO) is your instruction to buy. You issue it. It states what you want, at what price, in what quantity, delivered when. Once the supplier accepts it, it is a commitment on both sides.
• A purchase invoice (or supplier bill) is their claim for payment. They issue it. It states what they say they supplied and what they say you owe.

The PO is your intent. The invoice is their assertion. They should match, and checking that they do is the entire point of having both.

The three-way match

The discipline that makes this work is old and still undefeated:

1. The purchase order — what you agreed to buy, at what price
2. The goods received note — what actually arrived
3. The purchase invoice — what you are being billed for

If all three agree, pay it. If they do not, find out why before paying. That is it.

Most overbilling is not fraud. It is a price that crept up between order and invoice, a quantity billed in full when only part was delivered, a delivery charge nobody agreed to, or a duplicate invoice for a delivery already paid. All of it is caught by comparing three documents.

What a purchase order should contain

• A sequential PO number — this becomes the reference for everything that follows
• Supplier details and your delivery address
• Item descriptions, quantities, and agreed unit prices
• Required delivery date
• Payment terms
• Authorisation — who in your business approved this spend

That last line is what turns a PO from paperwork into a control. If a PO cannot be raised without approval, spending cannot happen without approval.

What to check on a purchase invoice

• Does it quote your PO number?
• Do the prices match the PO, line by line?
• Do the quantities match what was actually received, not what was ordered?
• Is the supplier's TRN present and correct?
• Is the VAT calculated correctly, and is this a valid tax invoice?
• Have you already received and paid an invoice for this delivery?

The VAT question matters directly to your money. In the UAE you can only recover input VAT where you hold a valid tax invoice. A supplier document missing the required content is not just untidy — it can cost you the recovery.

Why POs are worth the friction

Small businesses often skip purchase orders because they feel bureaucratic when the team is five people and everyone talks to each other. Then the business grows, three people are ordering from the same supplier, nobody knows what has been committed, and the first sign of a problem is a bank balance that does not match anyone's expectations.

Purchase orders answer questions that get very hard to answer later:

• What have we committed to spend that has not been invoiced yet?
• Did we agree to this price?
• Who approved this?
• Has this delivery already been billed?

That first question — committed but not yet invoiced — never appears in your accounts at all unless you raise POs. It is real money you have promised and cannot see.

Doing the buy side properly

The reason the three-way match fails in practice is that the three documents live in three places: POs in email, deliveries in a notebook, invoices in a folder. Nobody compares them because comparing them is work.

Pyalm Books runs purchases as a full cycle — purchase orders, suppliers, bills, and expense tracking in the same system as your sales and stock. Input VAT is captured as bills are recorded, so it flows into your VAT return rather than being reconstructed at filing time, and received goods update inventory directly.

Need a one-off purchase order now? The free invoice generator has a purchase order mode alongside invoices, quotations and proformas.

See the purchases side of Pyalm Books | Create a purchase order