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Find errors in supplier invoices

Ostatnio sprawdzono 7 September 2026 · Ta strona jest dostępna w języku angielskim.

To find errors in supplier invoices, check the arithmetic first, then compare every line with the price list in force by item code, never by description. Errors come in eight kinds, from a wrong unit price to a missing credit note. Price Double Check does this by email: forward the invoice and the price list, get the differing lines back.

An invoice error is any line where what the supplier billed differs from what the supplier itself told you earlier, in a price list, an order confirmation or a pro forma. The reference is the supplier's own document, not your memory of a phone call. That is why the method below never asks you to type anything in: the evidence already sits in your mailbox, and the check is a join between two documents you already have.

The eight kinds of error a supplier invoice carries

We have compared 382 invoice lines from one real chain of documents (a sports-nutrition manufacturer selling to a Baltic distributor, which sells on to a retailer): 327 matched the price list exactly, 41 were real price differences, 14 could not be matched for legitimate reasons, and 0 were misread. The differences fall into eight kinds, and every kind in the table below occurred at least once in that chain or is a standard category in accounts-payable recovery audits.

The first kind is the expensive one. In the chain above, the single line at +17.75% added 47.76 to one delivery and ate 91% of that delivery's margin. The supplier had simply not sent the 2024 price list; the buyer paid the old invoices against a list that no longer applied. Nobody had noticed by hand, across four invoices.

The fourth kind is invisible on the invoice. A pack that shrinks at the same price does not change a single figure on the bill; the invoice does not print pack sizes at all. It shows only when the new price list is set against the previous one, which is why a check that reads invoices alone will never find it. The same is true of the price that quietly becomes the new normal: a bar billed at 1.26 from March while the list said 1.176, with 1.26 appearing on a list only in October.

How often supplier invoices contain errors

Published figures come mostly from vendors of accounts-payable software and from recovery auditors, so we quote them with their source rather than as fact. A survey by the Institute of Finance and Management (IOFM), as quoted by DocuClipper, puts the share of invoices containing an error at 39%. Ardent Partners' benchmarks, as summarised by Finofo, put a mid-market company's invoice exception rate (invoices that need a person to intervene) at 25 to 40% for the median and below 15% for the best quartile. Medius, an AP-automation vendor, cites 5% as the commonly accepted ceiling for an error rate and under 1% for the best performers.

On money rather than counts: PRGX, a recovery-audit firm, states that duplicate and erroneous payments affect 0.8% to over 2% of annual disbursements and that its audits typically recover one million for every billion of supplier spend, with pricing errors, duplicates and missed credits as the main causes. Those are post-payment figures for large companies with full accounts-payable departments. A distributor with three people and no matching system has no reason to expect fewer errors, only fewer people looking. The time to find errors in supplier invoices is before payment, not in a recovery audit two years later.

Our own figure from the validation chain is 41 real price differences on 382 lines, or 10.7%, with every one of the 11 invoices agreeing with its printed total to the cent. Read it as one chain, one supplier, not as an industry rate; its value is that every one of the 41 was found by the same mechanical rule and none was a misread.

The method to find errors in supplier invoices

Three rules do almost all the work. They are the same rules whether you run them in a spreadsheet, in an accounts-payable suite, or by forwarding the documents to us.

1. Check the arithmetic before anything else. Add the extracted lines and compare the sum with the printed total. If they differ by a cent, something was misread and no line comparison is trustworthy yet. In our chain, 11 of 11 invoices passed this gate, which is what makes the rest of the findings credible.
2. Join by item code, never by description. Of 442 lines in the full set, 335 carried a description that did not match the wording of the same item on the price list: one document says SUB9 SALTS, the other SUB-9 SALTS ELECTROLYTES. Codes also arrive with suffixes such as 5116_1, which have to be normalised.
3. Compare each line with the price list in force on the invoice date, and treat plus or minus one cent as rounding, not as an error. Price lists carry four decimals, invoices two. Without that tolerance a checker sends three false alarms per invoice and is switched off within a week.

What the method does not do is judge. Freight has no reference price anywhere, so it is shown as an amount and a share of the goods, not scored. A unit-of-measure collision (one box that is 240 units) is reported as a quantity difference, not called a short delivery. An item that appears on no price list is listed as unmatched with its amount, not silently dropped. We describe the whole method in compare an invoice with a price list and the order-side check in compare a purchase order with an invoice.

Where each kind of error is caught

Not every comparison finds every error. The table shows which pair of documents exposes which kind, and what you have to keep on file for it to work.

The last two rows are why a single-invoice check is not enough. The three versions of one invoice in our chain, all with the same date and totals of 3,472.70, 3,482.25 and 3,480.34, are one invoice with a version conflict, not three invoices. The credit note that followed cancelled exactly one of two versions of another invoice. Only a check that keeps every document it has seen can say that.

What comes back when you forward the documents

When you forward an invoice and a price list to your Price Double Check address, the reply is an email with five parts: what it read (which documents, which supplier, which dates), the arithmetic gate (line sums against printed total), a table of the differing lines with code, description, quantity, billed, expected, delta and whether it is in your favour or against you, the lines it could not match with their amounts, and what to send to get more. The reply for one invoice is immediate when the price list is on file; the price-list-to-price-list and invoice-to-invoice comparisons come as a digest, because they only exist across documents.

• Nothing is typed in and no price list is loaded into a system; the list is the file the supplier emailed.
• Matching is deterministic and by code, so the same two documents always give the same answer.
• A difference is shown, not judged; the decision to dispute it stays with you.
• Documents are counted, not pages or emails: 10 a month free, 100 for 29 euro, 500 for 79 euro.

If you have been reading invoices with a chat model or an extraction tool, a parser is not an answer explains why extraction alone does not find errors: the finding is in the join, not in the reading.

Forward one invoice and the price list to your address and the differing lines come back by email, with the arithmetic checked first.