Time between two dates

Hi I am trying to get the time diff between oage and load and a button click...following is my code but my time span is not shoowing correct minutes...
Thanks:
using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;

public partial class date : System.Web.UI.Page
{
    DateTime start = new DateTime();
    DateTime end = new DateTime();

    protected void Page_Load(object sender, EventArgs e)
    {
        if (!Page.IsPostBack)
        {
         & ...