Dates swapped after a bank import? How to fix DD/MM vs MM/DD for good

If transactions land in the wrong month after an import, or some dates are rejected while others go through, the file almost certainly mixes day-first and month-first dates.

Why it happens

03/09/2026 means 3 September in South Africa, the UK, Australia and most of the world, but 9 March in the US. A bank exports in its own country's order. Excel then "helpfully" converts some cells to real dates using your computer's region and leaves others as text. The result is a column where some dates are day-first, some are month-first and some are text.

Accounting software then reads the column with one rule, so:

• dates where the day is 12 or less import in the wrong month, silently;
• dates where the day is 13 or more are rejected or import as nonsense.

How to spot it

Sort the imported transactions by date. If a statement for September suddenly has transactions in March, June and December, or the running balance never matches the bank, dates were swapped.

Before importing, look for any date where the first number is above 12. If the file has 25/09/2026, it is day-first. If it has 09/25/2026, it is month-first. A file with both is mixed and must be fixed row by row.

How to fix it

1. Keep the raw export as text: open the CSV with a text editor, or import it in Excel with the date column set to Text, so Excel doesn't reinterpret it.
2. Decide the order from rows where the day is above 12.
3. Rewrite every date in one unambiguous format such as YYYY-MM-DD (2026-09-03), or the exact format your software's import screen expects.
4. In QuickBooks Online, choose the matching date format on the mapping screen. In Xero, the order must match your organisation's region.

The automatic way

Rowvio reads every date format it finds (3/9/26, 03-Sep-2026, Sep 3, 2026, 2026-09-03, even Afrikaans month names), works out the order from the unambiguous rows and your region, warns you when a file is genuinely ambiguous, and writes one format your destination accepts. The preview shows every date it changed before you download.