Date input tag helper is not showing the date from database

The problem is that attribute [DataType(DataType.Date)] on your model property makes the input tag helper produce type="date" HTML attribute, which in HTML5 causes fixed, standard format - see information here: Is there any way to change input type="date" format?

In order to display the field with proper format, remove [DataType(DataType.Date)] attribute and you will be fine. Additionaly, in order to have forward slashes in date format, you need to escape them like this:

[DisplayFormat(DataFormatString = @"{0:dd\/MM\/yyyy}", ApplyFormatInEditMode = true)]
public DateTime OprettetDato { get; set; }

If you want to have custom date format with datepicker, you need to use some custom JavaScript solution.

Update: Later versions of tag helpers default to the input date type if the model property is a DateTime object. To allow a custom date format ensure that the html input type is text by adding [DataType(DataType.Text)]

Here is the solution to my problem

https://forums.asp.net/t/2167833.aspx?Date+control+is+not+showing+value+from+model

[DisplayFormat(ApplyFormatInEditMode = false, DataFormatString = "{0:dd/MM/yyyy}")]

ApplyFormatInEditMode = false