Entry point to every page is Page_Init(), and the exit point after loading is Page_PreRender(), so here is the code
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private DateTime _start;
private DateTime _end;
protected void Page_Init(object sender, System.EventArgs e)
{
_start = DateTime.Now;
}
protected void Page_PreRender(object sender, System.EventArgs e)
{
_end = DateTime.Now;
TimeSpan time = _end.Subtract(_start);
lblPageLoadTime.Text = string.Format("Page loaded in {0} seconds.", time.TotalSeconds.ToString());
}
/******************Source Code****************************/