Guide
Checking converted bank transactions before you trust them
Updated
Bank statement conversion has an unusually good property compared with other extraction jobs: the document contains its own checksum. Using it turns a leap of faith into a two minute verification.
Reconcile to the balance
Take the opening balance, add every credit and subtract every debit from the converted file, and compare against the closing balance on the statement.
If it matches, you have simultaneously confirmed that no transaction is missing, no amount was misrecognised, no row was duplicated and the debit and credit columns were not confused. No other single check does that much.
What a mismatch tells you
A difference equal to exactly one transaction means a missing or duplicated row, usually at a page boundary.
A difference that is a multiple of nine often means transposed digits. A difference that is exactly twice a transaction amount usually means a debit recorded as a credit. And a difference of a suspiciously round factor of ten points at a decimal point that moved during recognition.
What reconciliation does not catch
Wrong dates, which do not affect the sum but ruin any period-based analysis, and are the most common surviving defect.
Corrupted descriptions, which matter if the data is being categorised. And transactions attributed to the wrong account when several statements were converted together, which is invisible in each file and obvious in the total.
Spot check the descriptions
Take five rows from the middle of the file and compare them to the original by eye, including the reference text rather than only the amounts.
Descriptions are where wrapped lines and truncation show up, and where a reading-order error produces a complete, plausible file with the wrong reference against each amount.