My Excel account is to Microsoft 365 an not Office 2021

Activate Excel with the Microsoft account that owns Office 2021, and if Excel was installed from the Mac App Store, replace it with the Office 2021 installer downloaded directly from Microsoft.

1. Verify the license and account

1. In Excel, select Excel > About Microsoft Excel.
2. Check the displayed license:
   • Office 2021 means the correct perpetual license is active.
   • Microsoft 365 means Excel is using the wrong license. Microsoft documents this same check under Word > About Word.^1^
3. Sign in at https://account.microsoft.com/services using the Microsoft account used when Office 2021 was purchased or redeemed.
4. Confirm that Office 2021 appears under that account. If it does not, try the other email addresses that may have been used for the purchase.

Because Word is working, compare the account shown in Word with the account shown in Excel. In Excel, sign out of the housemate’s Microsoft 365 account and sign in with the account holding your Office 2021 purchase.

2. Check whether Excel came from the Mac App Store

A one-time Office license cannot activate Word, Excel, or PowerPoint downloaded from the Mac App Store. Those copies require a Microsoft 365 subscription and enter reduced-functionality mode—allowing files to open but preventing editing or saving.^2^

If Excel was obtained through the App Store:

1. Quit all Office applications.
2. Open Finder > Applications.
3. Control-click the Office applications and select Move to Trash.
4. Download the Office 2021 for Mac Installer directly from Microsoft: Office 2021 for Mac Installer
5. Run the downloaded package.
6. Open Excel and sign in with the Microsoft account that owns Office 2021.
7. Recheck Excel > About Microsoft Excel, then test Save As using a new blank workbook.

This reinstall does not delete your Word or Excel documents, but it replaces the Office applications.

3. If Excel still selects Microsoft 365

Reset the cached Office licenses. This removes licensing information for all Office applications, so first ensure that the Office 2021 account credentials are available.

1. Quit Word, Excel, PowerPoint, Outlook, and OneNote.
2. Download Microsoft’s license removal tool.
3. Open the downloaded .pkg file.
   • If macOS reports an unidentified developer, Control-click the file > Open.
4. Select Continue, complete the wizard, and provide the Mac administrator password when requested.
5. After the tool reports that the licenses were removed, open Excel.
6. Sign in using the account that owns Office 2021. If offered multiple licenses, select the one-time Office 2021 license.
7. Restart the Mac after activation.^3^

Finally, confirm that Excel > About Microsoft Excel shows Office 2021 and that a new workbook can be saved locally.

References

1. Update Microsoft 365 or Office on your macOS or iOS device | Microsoft Support
2. Microsoft Office activation and the Mac App Store | Microsoft Support
3. How to remove Office license files on a Mac | Microsoft Support