Extract base URl from a string in c#?

You can use URI class to get the host name.

var uri = new Uri("http://www.example.com/mypage/default.aspx");    
var host = uri.Host;

Edit You can use uri.Scheme and uri.Port to get the .Scheme e.g. (http, ftp) and .Port to get the port number like (8080)

string host = uri.Host;
string scheme = uri.Scheme;
int port = uri.Port;

You can use Uri.GetLeftPart to get the base URL.

The GetLeftPart method returns a string containing the leftmost portion of the URI string, ending with the portion specified by part.

var uri = new Uri("http://www.example.com/mypage/default.aspx");    
var baseUri = uri.GetLeftPart(System.UriPartial.Authority);

The following examples show a URI and the results of calling GetLeftPart with Scheme, Authority, Path, or Query, MSDN. enter image description here

Short Answer

myUri.GetLeftPart(System.UriPartial.Authority)

Long Answer
Assuming "Base URI" means something like http://www.example.com, you can get the base uri like this:

var myUri= new Uri("http://www.example.com/mypage/default.aspx");    
var baseUri = myUri.GetLeftPart(System.UriPartial.Authority)

This gives: http://www.example.com

Note: uri.Host gives: www.example.com (not including port or scheme)

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