gistfile1.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Threading;
using System.Diagnostics;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        private Stopwatch _timer = new Stopwatch();
        private int _total = 100;
        private int _current = 0;


        private void button1_Click(object sender, EventArgs e)
        {
            backgroundWorker1.RunWorkerAsync();


        }

        private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
        {
            _current = 0;
            _timer.Reset();
            _timer.Start();
            for (int i = 0; i <= _total; i++) // It's <= not <. You might be missing this
            {
                backgroundWorker1.ReportProgress(i);
                Thread.Sleep(500);
                _current++;
             
            }
            _timer.Stop();

        }

        private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)
        {
            progressBar1.Maximum = _total;
            progressBar1.Value = e.ProgressPercentage;
            if (_timer.IsRunning && _current > 0)
            {
                float elapsedMin = ((float)_timer.ElapsedMilliseconds / 1000) / 60;
                float minLeft = (elapsedMin / _current) * (_total - _current);
                TimeSpan eta = TimeSpan.FromMinutes(minLeft);
                label1.Text = eta.ToString();
            }
        }

        private void button1_Click(object sender, EventArgs e)
        {
            backgroundWorker1.RunWorkerAsync();
        }

    }
}