How to calculate financial year in c# asp.net web form

Question

I have an sql table that returns financial year start_date and end_date, so now i want to use that query to dropdownlist of months starting from april until march. And based on the selected month i get the revenue for that month.So the query for calculating financial year only return 2018/04/01 as start_date and 2019/03/31 as end_date, so bare in mind it's not months, just a date .Of course i will be connected to a server and choose my database and table. see what i tried below.

public class Fyear
{
    public string FiscalY_Start { get; set; }
    public string FiscalY_End { get; set; }
}

protected void Page_Load(object sender, EventArgs e)
{
    //Data Source=cntrra02-sql-rs;Initial Catalog=Training_Database;Integrated Security=True
    DateTime start_date;
    DateTime end_date;

    List<Fyear> list = new List<Fyear>();


    if (!Page.IsPostBack)
    {
        SqlConnection con = new SqlConnection(@"Data Source=serv_name;Initial Catalog=Database_name;Integrated Security=True");
        SqlCommand cmd = new SqlCommand(@"SELECT [ST_FI], [END_FY] FROM [FiscalYear]", con);
        con.Open();
        SqlDataReader rdr = cmd.ExecuteReader();

        while (rdr.Read())
        {
            start_date = Convert.ToDateTime(rdr["ST_FI"]);
            end_date = Convert.ToDateTime(rdr["END_FY"]);
            //DropDownList1.Items.Add(start_date.ToString());
            //int count = 0;
            while (start_date <= end_date)
            {
                //count++;
                //list.Add(new Fyear{ FiscalY_Start = start_date.ToString("MMMM")});
                start_date = start_date.AddMonths(1);
                DropDownList1.Items.Add(start_date.ToString());
            }
        }

         SqlDataAdapter sda = new SqlDataAdapter(cmd);
         DataTable dt = new DataTable();
         sda.Fill(dt);
        // DropDownList1.DataSource = dt;
        // DropDownList1.DataBind();
    }