File Sharing Problems

How to Fix Word Mail Merge Date Formatting and Excel File Locking

Maira Mehtab Sep 22, 2026 869 views

Question details

The user needs to understand why Excel dates appear as numbers during a Word mail merge, how to prevent the Excel data source from being locked, and how to edit free-text fields dynamically while the merge is running.

Product: Word and Excel
Device & OS: not provided
Scenario: Running a mail merge in Word using an Excel workbook as the data source.
Observed behavior: Excel dates display as raw numbers in Word when the workbook remains open, the source file becomes locked for editing, and standard merge fields do not allow on-the-fly text customization.

Before you start

Ensure your Excel data source is fully updated, saved, and completely closed before attaching it to your Word mail merge document to prevent file locking and formatting errors.

Solution 1Recommended

Close and Prepare the Excel Workbook Before Merging

Prevent OLE DB file locking and date formatting anomalies by finalizing and closing the Excel data source before starting the mail merge in Word.

In Microsoft Office, dates appearing as numbers when the workbook is open has been a known mail merge behavior since Excel 2007. Furthermore, the workbook is locked by the system whenever it is attached to a mail-merge main document before being opened.

Format data in Excel

Open your Excel workbook and verify that all dates and data fields are formatted correctly for your mail merge.

Save and close

Save all required changes to the Excel file, then completely close the workbook.

Attach to Word

Open your Word document and attach the closed Excel file as your mail merge data source.

Known Behavior: Make all required changes to the Excel file before using it as the data source. If you attempt to open or edit the Excel file while it is attached to the active Word merge document, it will open as Read-Only.

Solution 2

Use a FILLIN Field for On-the-Fly Text Customization

Use the special FILLIN field code in Word to prompt the user for customized text during the mail merge process without modifying the original Excel data.

Free Microsoft Office alternative

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Frequently Asked Questions

Why are dates from my Excel file showing as plain numbers in Word?

This is a known behavior in Microsoft Office dating back to Excel 2007. If the Excel workbook remains open while the Word mail merge is running, the connection may read dates as their underlying serial numbers. Completely close the Excel file before starting the merge to fix this.

Why does my Excel data source say it is locked for editing?

The workbook becomes locked because it is actively attached to a mail-merge main document in Word. You must close the Word document to release the lock before you can make any changes to the Excel file.

How do I type the curly braces for a FILLIN field in Word?

You cannot type the curly field braces manually using standard keyboard characters. You must press the Ctrl+F9 keys in Word to insert the functional field braces, and then type your field codes inside them.

Will changes made using the FILLIN field update my original Excel file?

No. The text you enter into a FILLIN prompt during the mail merge process is only applied to the final merged document. It does not overwrite or alter the data in your original Excel source file.

Document & File Issues