3-way matching is one of the oldest controls in accounts payable, and one of the most commonly implemented badly — usually as a manual checklist someone works through under deadline pressure, which defeats the point of having a control at all. The idea itself is straightforward: three documents, each answering a different question, cross-checked before money moves.
The three documents
The purchase order (PO) answers “what did we agree to buy, and at what price?” It’s the commitment, created before anything ships.
The goods receipt (GRN) answers “what did we actually receive?” It’s created when the delivery arrives, and it’s the document most likely to differ from the PO — partial shipments, quantity short-ships, and damaged-goods deductions all show up here first.
The vendor bill answers “what is the vendor asking to be paid for?” It should agree with both of the above, but it’s the vendor’s own document, submitted independently of your internal records.
3-way matching means checking that all three agree — quantity, price, and item — before the bill is approved for payment.
Why tolerances matter
Requiring an exact match across all three documents sounds rigorous, but in practice it breaks constantly, because small variances are normal: a shipment arrives one unit short and gets completed in a second delivery, or a price differs by a rounding amount after a currency conversion. A matching system with zero tolerance either blocks legitimate invoices constantly or gets its checks quietly overridden by whoever’s under the most deadline pressure — neither outcome is a real control.
Configurable tolerances solve this by defining what counts as “close enough” — a percentage or absolute variance on price, a unit threshold on quantity — so ordinary variance clears automatically and only genuine discrepancies get flagged for a human to look at.
What happens when something doesn’t match
The output of a mismatch shouldn’t be silent approval or silent rejection — it should be a flag, with enough context (which document disagreed, by how much) for someone to resolve it quickly. That’s the difference between 3-way matching as a real control and 3-way matching as a rubber stamp: what happens on the exception path, not what happens when everything lines up.
Where this fits in the broader AP workflow
3-way matching sits between invoice extraction and approval routing — the invoice has to be read and structured before it can be matched, and matching has to clear before it goes to an approver. See how the full pipeline runs end to end, or how it’s built specifically for Tally Prime users.