Hi JP — thanks, I can help. Your description (works for the first ~22 rows then “reverts” to US-style) sounds like a formatting / locale detection issue in Excel rather than a bug in your typing. A few different things can cause that behavior depending on whether you type the dates, paste them, or import a CSV. Below I give short explanations and specific step-by-step fixes for the common situations. Try the ones that match how you create the dates and tell me what you see.
Quick checks first
- Are you typing the dates directly into Excel, or pasting/importing them from another program or a CSV file?
- Which Excel version (e.g., Excel for Microsoft 365, Excel 2019) and Windows 11?
- If you can, try this quick test: in a new blank workbook select column A, format it (steps below) to dd-mm-yy, then type 01-01-25, 02-01-25 … down 30 rows. Do the first 22 remain dd-mm-yy and the rest change? Tell me the result.
Solutions (pick the one that matches your situation)
A — If you are typing dates manually
- Select the whole column where you enter dates (click the column header).
- Press Ctrl+1 → Number tab → Category = Date. In the “Locale (location)” dropdown choose French (France) or French (Canada) depending on which French format you want. Pick the dd-mm-yy style. Click OK.
- Or use Custom and enter: dd-mm-yy (or dd-mm-yyyy).
- Now enter your dates. Excel will store them as dates and display them in dd-mm-yy for the entire column.
B — If some entries are stored as text or mixed types (causes formatting to not apply)
- Select the column. Data → Text to Columns → Delimited → Next → Next. On the last screen set Column data format = Date and choose DMY from the dropdown → Finish.
- This converts text-formatted dates to real Excel dates using day-month-year order.
- Then apply the custom date format (Ctrl+1 → Custom → dd-mm-yy).
C — If you’re pasting from another app or importing a CSV
Excel (or Power Query) often “guesses” the column data type by sampling the first rows. If the sample contains only dd-mm entries Excel may treat later ambiguous entries differently.
If opening a CSV by double-click:
- Instead of double-clicking the CSV, use Data → Get Data → From Text/CSV → select the file. In that import window pick “File Origin” and in the preview step set the Locale/Region to French (or choose “Load with Power Query”). In Power Query Editor right‑click the date column → Change Type → Using Locale → choose Date and Locale = French. Then Close & Load.
If you paste:
- Paste into a column already formatted as Date (see A), or paste into Notepad first and then copy → paste into Excel to avoid hidden formatting bringing US-style dates.
D — If you are using an Excel Table
- If your range is an Excel Table (Insert → Table), set the format on the column header cell (Ctrl+1) — the Table should propagate the format to the new rows automatically. If some rows are already text, convert them first (use Text to Columns as in B).
E — Office / Windows locale settings (if Excel keeps ignoring your choice)
- In Excel: File → Options → Language. Make sure French is listed as an Editing language and (optionally) set it as default.
- In Windows 11: Settings → Time & language → Language & region → set Regional format to French (Canada) or French (France) and check Short date format. Changing Windows region can affect Excel’s interpretation of ambiguous dates.
Why “about 22 rows” might happen
- Some import/data-detection tools sample only the first N rows to decide a column type. If the first N rows all look like a certain format Excel/Power Query may set the column type and then later rows that don’t match get interpreted differently. That’s why forcing the column format (select column → Ctrl+1) or using Text to Columns / Change Type Using Locale fixes it.
If the above doesn’t fix it
- Tell me: do you type, paste, or import? Share the exact string you type for dates (example: 1/2/25 or 01-02-25). I can then give the precise steps. If you’re comfortable attaching a tiny sample workbook or a screenshot (no private data), attach it and I’ll look — note: I didn’t receive any attachment with your post, so please try uploading again if you meant to attach something.
Safety tip
- Make a copy of your worksheet before doing bulk conversions (Text to Columns, power-query loads), so you can revert if the result isn’t as expected.
If you want, I can give the exact step-by-step to import a CSV with French dates or the exact menu clicks for your Excel version — tell me which scenario and which Excel version and I’ll walk you through it.