Here, that should be easy
private void Days()
{
DateTime dt1 = DateTime.Today;
DateTime dt2 = DateTime.Today.AddDays(14);
lbl_borroweddate.Text = dt1.ToShortDateString();
lbl_duedate.Text = dt2.ToShortDateString();
TimeSpan ts = dt2 - dt1;
double days = (ts).TotalDays;
}
solved How can I calculate difference between two dates? [duplicate]