Claude Excel keeps messing up my dates in Excel Sheet desktop online same issue

https://preview.redd.it/iqw4k6stojyg1.png?width=412&format=png&auto=webp&s=a56ac06be9c993f153cbf585f67bb4d3f3ff1fba

Hi, I’m having an issue with dates in a spreadsheet where Claude excel extracts them from some source data (such as a paste directly into the chat or a paste into a different sheet) then adds to a spreadsheet in a messy way where they are frequently getting mixed up between day and month e.g UK vs US format or store as text.

Claude excel thinks the problem is that when dates are added by the add-in, the system stores them in a way that doesn’t always keep the day/month order. So if the day is 12 or lower, it can flip them, for example, 4 June 2026 might turn into 6 April 2026. There’s no error, it just ends up as the wrong date.

Or it keeps giving me garbage answers like (but not limited to, other versions include things about serial number formats) the following;

The format property still shows m/d/yy throughout — but crucially, every single cell's display text is already showing correct UK format (e.g. 30/07/2025, 06/01/2026). This is Excel's regional locale doing the right thing regardless of the format code.

So the short answer: visually it's correct — everything displays as dd/mm/yyyy. The underlying format code just stubbornly reports as m/d/yy because your Excel's regional settings override it to UK display anyway.

The dates you were seeing as "future" earlier were genuinely just the US format code causing visual confusion — that's now resolved. All 270+ date cells are displaying in UK order. Do you want me to force the format code to properly say dd/mm/yyyy across the whole column regardless, or move on to the next task?

I say garbage because the issue will literally occur when I ask it to add another date manually or extracted! I've even spent hours fixing the errors in a separate sheet them pasting them back into a new cell only to have it happen all over again with a new entry or (or possibly after sorting but not sure)

I’ve tried saving the dates as text (like "04/06/2026"), which stops the mix-up, but then I can’t sort the dates properly or use them in formulas.

I have used the paid excel desktop version to see if it would use my systems date settings as per research but it's still messing up the dates and this is a large amount of data.

Is there a simple way to keep dates in the correct day/month format while still being able to sort them and use them normally?

Or is there a better way to handle this?

Is this s known issue?

I’m using a UK date format.