Formatting Issues

How to Fix Excel Dates Changing from UK to US Format When Emailed

Natalie Taylor Oct 8, 2026 868 views

Question details

The user needs to prevent Excel dates from automatically changing from the UK format (DD/MM/YY) to the US format (MM/DD/YY) when a workbook is attached to an email.

How to Fix Excel Dates Changing from UK to US Format When Emailed

Product: Standalone Microsoft Excel
Device & OS: Windows
Scenario: Attaching an Excel workbook synchronized with OneDrive to an Outlook email to send to another user.
Observed behavior: Dates originally formatted and displayed as UK DD/MM/YY in Excel appear as US MM/DD/YY after the file is sent as an email attachment and opened by the recipient.

Before you start

Before troubleshooting, verify whether the dates in your spreadsheet are entered as actual date values (which align to the right by default) or as plain text, as this determines how Excel handles the formatting across different computers.

Solution 1Recommended

Apply an Explicit Custom Date Format

Set a custom date format to lock the display structure to the UK style (DD/MM/YY), ensuring it won't change based on the recipient's system default settings.

By default, Excel uses short date formats tied to the computer's regional settings. Applying a custom format overrides this behavior, forcing the date to display exactly as formatted regardless of who opens the file.

Select the date cells

Open your workbook in Excel and highlight the column or specific cells containing the dates you want to format.

Open the Format Cells dialog

Right-click the selected cells and choose 'Format Cells' from the context menu, or press the keyboard shortcut Ctrl+1.

Apply a custom format

Navigate to the 'Number' tab and select 'Custom' from the Category list on the left.

Define the UK format

In the 'Type' input box, enter 'dd/mm/yy' or 'dd/mm/yyyy'. Click 'OK' to apply the formatting, and save the workbook before attaching it to your email.

Format Locked: Applying a custom format ensures the date retains its visual structure permanently, preventing Outlook or OneDrive from displaying it differently on other devices.

Solution 2

Verify Windows Regional Settings

Ensure that the operating system's region is correctly set to the UK on both the sender's and recipient's computers, as Excel defaults to system settings when displaying standard dates.

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Frequently Asked Questions

Why do Excel dates change format when I email them?

Excel stores dates internally as serial numbers and displays them based on the regional settings of the device opening the file. If the recipient's computer uses US regional settings, standard dates will automatically display as MM/DD/YY instead of the UK DD/MM/YY format.

Does Outlook change the date format in Excel attachments?

No, Microsoft Outlook does not alter the cell formatting of attached files. The visual change happens because the file is being opened on a computer with different regional settings, or because cloud synchronization tools like OneDrive default to a different region online.

How can I tell if my dates are formatted as text or true dates?

Select the date cells and observe their default alignment in the spreadsheet. True date values automatically align to the right side of the cell, whereas text aligns to the left. You can also test this by changing the cell format to 'General'; a true date will turn into a 5-digit serial number (e.g., 44000).

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