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Editorial Team
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Asked: 2026-05-23T08:00:32+00:00

When generating an Excel XML workbook with ASP.NET i’m appending 3 cells in a

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When generating an Excel XML workbook with ASP.NET i’m appending 3 cells in a row like:

sb.Append(String.Format(
"<Cell><Data ss:Type=\"DateTime\">{1}</Data></Cell>{0}",
Environment.NewLine, 
item.DateAvailable.ToString("yyyy-MM-ddTHH:mm:ss.fffffffK")
)); // newlines added for readability;

item.DateAvailable is a C# DateTime that has to end in Excel as An cell-DateTime.

so

value from debug in VS2010 in asssembly:

 2011-08-15T01:16:06.8470000

value in excel:

 40761,2299142361

after manual conversion of the cell formatting:

 6-08-11 5:31

However, when converting it outputs in excel as a number, and the cell formatting is set to custom. When I manually change the cell formatting back to DateTime the correct??? date is shown in the correct format. But of course, the business would not accept such a raw data they have to convert themselves 😉

Perhaps I am using the wrong StringFormat?

What is the correct format to write a DateTime in this case and output it in Excel in the correct DateTime Format?

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1 Answer

  1. Editorial Team

    Yes, you are using a “wrong” string format, i.e. a format that Excel does not automatically recognize (or parse appropriately) as a date. Drop the T. Also, the date-time format in Excel rounds at least to milliseconds, if not to integer seconds, so you might as well drop some of those decimal places.

    This should work:

    item.DateAvailable.ToString("yyyy-MM-dd HH:mm:ss.ffff")
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