Date entered is changed to a different date

Recent Microsoft 365 Windows builds introduced:

• A new internal date/time parser
• Partial unification with Power Query / Power BI logic
• Side effects where slash-based dates are misinterpreted as numeric tokens

This bug only shows up when:

• System locale = US
• Excel language = US
• Date format = MM/DD/YYYY
• Auto-conversion is enabled

That exact combo explains why:

• Two Windows PCs fail
• macOS Excel works
• Husband’s Windows Excel works (slightly different settings/build)

Disable Excel’s broken auto date parsing

Step-by-step (important: do this exactly)

1. Open Excel
2. File → Options → Advanced
3. Scroll to Editing options
4. UNCHECK:

• Automatically convert numbers to dates
• Use system separators (temporarily)

      5. Click OK

      6. Close Excel completely

      7. Reopen Excel and test

This forces Excel to stop using the new parser.

If that option does not exist (some builds hide it)

Use this workaround that never fails:

Force Excel to treat entries as real dates

Format the column as Custom, not Date:

mm/dd/yyyy

(Custom ≠ Date category)

You are not imagining this 🙂

It is not your laptops

It is not corruption

Reinstalling Excel probably won’t help

This is a real regression in recent Excel for Windows

Disabling auto date parsing or forcing Custom format fixes it

My answers are voluntary and without guarantee!

Hope this will help you.