Excel provides many options for displaying numbers in different formats like percentages, currency, and dates. If the built-in formats don’t work for your needs, you might want to create a custom number format.
You can’t create custom formats in Excel Online but if you have the Excel desktop application, you can use the Open in Excel button to open the workbook and create them.
Click Open in Excel.
See this article on creating custom number formats in Excel.
For news about the latest Excel Online updates, visit the Microsoft Excel blog.