Microsoft 365 Excel Issue

Thanks for sharing the details! Excel Calculation Mode Is Set Per-Workbook

On macOS, Microsoft Excel stores calculation mode inside each workbook, not globally.

Fix

• Open the affected workbook
• Go to Excel → Preferences
• Select Calculation
• Set Calculation Mode to Automatic
• Uncheck “Save calculation results”
• Close Excel completely
• Reopen the file

This resolves the “formulas stopped calculating after 1/1/26” symptom most of the time.

See if this helps. If you need further assistance just let me know.

Best regards,

Kimberly

If Microsoft 365 Excel is not calculating formulas on spreadsheets after 1/1/26, it may be related to how Excel handles dates and calculations. Excel has known issues with certain formulas and date handling, particularly with custom functions or external links that may not update correctly when opened in different versions.

To troubleshoot this issue, consider the following steps:

1. Check for Updates: Ensure that your Microsoft 365 is up to date. Sometimes, updates include fixes for calculation issues.
2. Recalculate Workbooks: You can force Excel to recalculate all open workbooks by pressing CTRL + ALT + F9. This can help if the formulas are not updating as expected.
3. Review Formulas: Look for any custom functions or formulas that may not be referencing the correct ranges or that depend on cells not explicitly included in the function. You may need to modify these functions to ensure they calculate correctly.
4. External Links: If your workbook contains external links, ensure that the source workbooks are accessible and that the links are updated correctly. Errors in external links can cause calculation issues.

If these steps do not resolve the issue, you may want to consult the Microsoft support documentation or community forums for further assistance.

References:

• Custom function may not calculate expected value in Excel
• External links may be calculated when you open a workbook that was last saved in an earlier version of Excel