How to record a purchase order number in your ledger

A purchase order number is small data with outsized value. It is the thread that ties a commitment you authorised to the invoice that eventually arrives, and then to the asset or expense it bought. In this article we cover where the number belongs, how it cross-references with Accounts Payable, and what to do when the paperwork does not line up.

What is the purchase order number for?

The PO number is your internal authorisation reference. When you enter it against a purchase, or against a fixed asset acquired under a PO, you create a cross-reference that lets anyone trace the transaction in three directions: to the original requisition, to the supplier invoice in Accounts Payable, and to the goods-received record.

That trace is what makes the number worth capturing. At month-end, when you are matching open POs against received invoices, the number is the join key. Without it, matching becomes a manual hunt through amounts and dates.

Where does the number go in the entry?

The PO number is reference data, not an accounting field. It does not affect the debit or credit. Enter it in the reference or PO field of the bill, purchase, or asset transaction, wherever your ledger provides one.

For a fixed asset bought under a PO, record the number on the asset acquisition entry. This supports reporting later, when you need to show which authorisation approved the capital spend. Keep the number exactly as issued, including any leading zeros, so the cross-reference matches on both sides.

How does the PO number link to Accounts Payable?

When the supplier invoice arrives, it should quote your PO number. Enter the bill in Accounts Payable with that same number in the bill's reference field. The two records now share a key.

Three-way matching then becomes mechanical: PO, goods-received note, and invoice. Quantities and prices on the invoice should agree to the PO. If the supplier billed without quoting the PO, add it yourself from the commitment record rather than leaving the field blank, and note that the supplier omitted it.

What if the PO and the invoice disagree?

Discrepancies are common and are a judgement call, not an error to force through. If the price differs, check whether the PO had a later amendment. If quantities differ, check the goods-received record before paying either figure.

If the invoice is genuinely for something no PO covers, do not attach it to an unrelated PO to keep the ledger tidy. Record it on its own merits and flag it for approval, because it represents unauthorised spend until someone with authority accepts it.

What if there was no purchase order at all?

Many businesses raise POs only above a threshold, or only for stock and capital items. Where no PO exists, leave the field empty rather than inventing a number. A fabricated reference is worse than none, because it breaks trust in every other reference.

For spend that skips the PO process, the invoice approval itself is the authorisation evidence. File it so the approver is identifiable, which is the control the PO would otherwise have given you.

A short worked example

Suppose your operations team raises PO 2041 for three monitors at 180 each. The supplier invoices three monitors at 180, quoting 2041. You enter the bill in Accounts Payable with 2041 in the reference field, match it to the PO, and the commitment clears.

Now suppose the invoice quotes 2041 but bills four monitors. The goods-received note shows three were delivered. You match three lines and query the fourth before payment, and the PO stays open for the disputed item until it is resolved. That is the PO number doing its job: it made the mismatch visible instead of buried in an amount.