Why supplier invoice totals don't match the accounting system

A folder of supplier invoices totals differently from the ledger for the same period, and the difference is not a round figure that points at anything obvious. This is common — and it is almost never one large mistake. It is usually several small structural causes stacked together. Here they are, in the order worth checking.

01 · The same expense is in the folder twice

Where documents arrive through more than one channel — emailed PDFs, scanned paper, photographs — the same expense will eventually arrive through two of them. Nothing about the two files matches: different names, different dates received, one crisp and one photographed at an angle. Deduplication by filename or file hash cannot find them, because they genuinely are different files containing the same fact.

The check — group by supplier and amount with a few days’ tolerance on date, and review every group with more than one member. Match on the amount, not the filename.

02 · Something in the folder is not an invoice

A folder named for invoices collects whatever looks financially relevant: payment confirmations that restate a paid invoice, quotes and pro-formas for work that may never have happened, and occasionally a document from a different transaction entirely — a closing statement or loan schedule carrying a figure far larger than any invoice present.

The check — before summing, sort by amount descending and open the top ten documents. Anything an order of magnitude above a typical invoice deserves examination.

03 · Tax is handled differently on each side

Invoice totals usually include tax; ledger expense figures usually exclude it, because recoverable tax sits in its own account. Comparing a tax-inclusive folder total against a tax-exclusive ledger figure produces a difference of roughly the tax rate — frequently the entire discrepancy, hiding in plain sight.

The check — compute the difference as a percentage. If it lands near your tax rate, this is the cause.

04 · Cut-off — period boundaries differ

An invoice dated the 29th, received on the 3rd, entered on the 7th and paid on the 20th has four plausible dates, and four answers to which month it belongs in. The folder is organised by one of those dates and the ledger by another, shifting documents across the boundary in both directions.

The check — pull everything dated within a week either side of the boundary and compare individually. The discrepancy is usually a handful of documents.

05 · Credit notes counted as costs

A credit note is a negative invoice. It looks like an invoice and is filed with the invoices; if its sign is not read correctly it is added rather than subtracted, distorting the total by twice its value.

The check — search for “credit”, “refund” and “adjustment”, and confirm each entry is negative in the total.

06 · The label on the document is imprecise

A field marked as a total may be a pre-discount total. A figure beside a tax label may be a registration number. A “balance” may be a running account balance unrelated to the invoice. Extraction that reads by label alone produces plausible, incorrect data — which is why dependable processes validate arithmetic instead: subtotal plus tax must equal total, and line items must sum to subtotal.

The check — for a sample of invoices, verify subtotal + tax = total from the extracted figures. Failures identify the documents where a label misled the extraction.

Working through it

Attack the difference in that order: duplicates and non-invoices usually account for most of it; tax treatment and cut-off explain most of the remainder.

What should not happen is an adjustment on either side without knowing which cause is present. A reconciliation that balances because the difference was plugged is worse than one that does not balance — it stops anybody looking. Where the folder is too large to check by hand, that is the point at which automating the checks justifies its cost: the arithmetic does not tire on document four hundred.