Date entered is changed to a different date

Helloiindy500​,   this isn’t file corruption.

Excel on your laptop is interpreting typed dates differentlydue to a date system or regional/locale mismatch, not the worksheet itself.

When you press Enter, Excel converts the entry to a numeric date serial and then displays it using the wrong system/locale, which is why dates jump to years like 1970 or 1963. When you type the slashes and it stays as entered, Excel is treating it as text.

What to check (quickly)

1. Windows Region & Date format
   Settings → Time & Language → Region
   Ensure the short date format matches what you type (e.g. MM/dd/yyyy).
2. Excel Date System
   Excel → File → Options → Advanced
   Make sure “Use 1904 date system” is unchecked.
3. Excel Language/Locale
   Excel → File → Options → Language
   Confirm the correct editing language is selected.

Restart Excel after changes.

Microsoft documentation

• Date systems in Excel
  https://support.microsoft.com/office/date-systems-in-excel-e7fe7167-48a9-4b96-bb53-5612a800b487
• Change the date system, format, or two-digit year interpretation
  https://support.microsoft.com/office/change-the-date-system-format-or-two-digit-year-interpretation-aaa2159b-4ae8-4651-8bce-d4707bc9fb9f

Once these settings are aligned, typed dates will behave normally again.

If you enter 01/01/2025 without the slashes it returns 10/29/4670.

If you enter 01/19/2026 without the slashes it returns 08/27/5163.

There must be something on your system which strips the slashes away right after input.

Thank you. I did manage to do what you documented and unfortunately it did not fix the issue. I will try again tomorrow in case I missed something. I ran office quick repair as well I 

so frustrating. I don’t understand why it was working right and now it is not. 

The issue you're experiencing with Excel altering dates is likely due to regional settings or date system mismatches between your laptop and your husband's. Here's a structured solution:

Root Cause Analysis

 1. Date Parsing Conflict:
Excel interprets dates based on your system's regional settings (e.g., MM/DD/YYYY vs. DD/MM/YYYY). If your laptop uses a different format than the file expects, entering 01/01/2025 (January 1st) might be parsed as 01/01/25 (Day 1, Month 1, Year 1925) if Excel misreads the separator.

 2. 1904 Date System:
If your Excel uses the 1904 date system (common on Macs), dates are stored as days since 1904-01-01. This can cause discrepancies when opening files created with the 1900 system (Windows default). For example:

• 01/01/2025 in the 1900 system = Day 45,678.
• In the 1904 system, this becomes Day 45,678 − 1,462 (days between 1900–1904) = 44,216, which converts to October 29, 1970.

 3. Corrupted Excel Settings:
A glitch in Excel’s settings or a recent update might break date parsing.

Step-by-Step Fixes

  1. Check Regional Date Format

• Windows Settings:
  Go to Settings > Time & Language > Region > Regional Format.
  Ensure the format matches your data entry (e.g., MM/DD/YYYY for U.S., DD/MM/YYYY for Europe).
• Excel-Specific Format:
  In Excel, go to File > Options > Advanced > Use 1904 Date System and uncheck it (Windows default).

 2. Force Excel to Recognize Dates

• Format Cells as Text First:
  Temporarily format the column as Text (right-click column > Format Cells > Text).
  Enter dates with slashes (e.g., 01/01/2025), then reformat as Date.
• Use DATEVALUE Function:
  If dates are already corrupted, use =DATEVALUE(A1) in a new column to convert text to dates.

 3. Reset Excel’s Settings

• Repair Office Installation:
  Open Excel → File > Account > Update Options > Repair.
• Delete Corrupted Preferences:
  Close Excel. Press Win + R, type %appdata%\Microsoft\Excel, and delete the Excel16.xlb file (back up first).

 4. Test in a New Workbook

Create a new Excel file and test date entry:

• If dates work, the issue is file-specific. Copy data into the new file.
• If dates still break, proceed to repair Excel.

 5. Disable Automatic Conversion

• Use Apostrophe Before Dates:
  Type '01/01/2025 to force Excel to treat it as text, then reformat.
• Turn Off AutoCorrect:
  File > Options > Proofing > AutoCorrect Options > Uncheck "Replace text as you type".

Why It Works on Your Husband’s Laptop

Your husband’s laptop likely uses:

• The 1900 date system.
• Regional settings matching the date format you’re using.
• A corruption-free Excel installation.

Prevent Future Issues

• Standardize Date Formats: Agree on YYYY-MM-DD (universal) or MM/DD/YYYY (U.S.).
• Use Data Validation:
  Go to Data > Data Validation > Date, and set allowed dates to avoid typos.
• Update Excel: Ensure both laptops are on the same build (e.g., Microsoft 365 vs. 2019).

By aligning regional settings, disabling the 1904 system, and resetting Excel, the issue should resolve. If problems persist, a full Office reinstall may be needed.

My answers are voluntary and without guarantee!

Hope this will help you.

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Hello iindy500​,

Excel is misreading your dates because of a mismatch between your Windows regional settings and Excel’s date system. Check your Windows Region → Regional format and make sure it matches the date style you’re using (MM/dd/yyyy vs dd/MM/yyyy).

Also confirm the column is formatted as Date in Excel. Using slashes (01/19/2026) instead of dashes helps. If it still misbehaves, run an Office Quick Repair.