Changing a date format in Excel changes how the date is displayed, not the stored date value. Formulas can keep using the same date while you show it as 6/9/2026, 09.06.2026, Jun 9, 2026, or another format.
Does this affect you?
Use this for Excel for Microsoft 365, Excel 2021, and Excel 2019 on Windows or Mac when dates look like serial numbers, appear in the wrong country format, or need a specific style for reporting.
Choose a built-in date format
Start with Excel built-in date styles.
- Select the date cells.
- Right-click and choose Format Cells, or press Ctrl+1 on Windows or Cmd+1 on Mac.
- Open the Number tab.
- Choose Date.
- Pick a Type such as 3/14/2026, 14-Mar-26, or March 14, 2026.
- Use Locale to see formats for another region, such as English (United Kingdom).
- Click OK.
Build a custom date format
Use this when the built-in choices do not match the required layout.
- Select the cells and open Format Cells.
- Choose Date first so Excel loads date examples.
- Choose Custom.
- Enter a format code in Type.
- Check the Sample preview.
- Click OK.
- mm/dd/yyyy shows 06/09/2026.
- dd.mm.yyyy shows 09.06.2026.
- yyyy-mm-dd shows 2026-06-09, useful for sorting and file names.
- mmm d, yyyy shows Jun 9, 2026.
- dddd, mmmm d, yyyy shows Tuesday, June 9, 2026.
More control
Understand the format codes
m, mm, mmm, and mmmm control month display. d, dd, ddd, and dddd control day display. yy and yyyy control two-digit or four-digit year display.
Fix dates showing as numbers
A value like 45678 is usually a real date formatted as General or Number. Apply a Date format to make it readable.
Fix ##### in date cells
Hash marks usually mean the column is too narrow for the date format. AutoFit or widen the column.
Change default regional date behavior
Excel follows the computer short date settings for new entries. On Windows, check Time & Language or Region settings. On Mac, check System Settings > General > Language & Region.
Avoid ambiguous typed dates
6/9/2026 means June 9 in the US and September 6 in many other regions. Use yyyy-mm-dd when entering dates that must be interpreted consistently.
Sources
- Microsoft Support – Format a date the way you want (2025)
- Microsoft Support – Change the date system, format, or language (2025)
- Microsoft Support – Number format codes (2025)