Set the start week to the monday.
//This will work on load event of form
dtm_end_week.Value = dtm_start_week.Value.AddDays(6);
//This will work on selecting dtm_start_week .
private void dtm_start_week_MouseEnter(object sender, EventArgs e)
{
dtm_end_week.Value = dtm_start_week.Value.AddDays(6);
}
Thanks