Hi JOYSON,

Refer below links and implement in your code.

Implement AutoIncrement ID in Table without setting Identity Column in SQL Server

[Solved] How to auto increment a column without using Identity in SQL Server

Refer the below sample.

<asp:TextBox ID="txtId" runat="server"></asp:TextBox>

C#

protected void Page_Load(object sender, EventArgs e)
{
    NewId();
}
 
private void NewId()
{
    SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings[1].ConnectionString);
    con.Open();
    SqlCommand cmd = new SqlCommand("SELECT MAX(EmployeeID) + 1 as Id FROM Employees", con);
    txtId.Text = cmd.ExecuteScalar().ToString();
    con.Close();
}

VB.Net

Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load
    NewId()
End Sub
 
Private Sub NewId()
    Dim con As New SqlConnection(ConfigurationManager.ConnectionStrings(1).ConnectionString)
    con.Open()
    Dim cmd As New SqlCommand("SELECT MAX(EmployeeID) + 1 as Id FROM Employees", con)
    txtId.Text = cmd.ExecuteScalar().ToString()
    con.Close()
End Sub

Output is display as increment by 1 each time based on database record on page load.

   protected void Page_Load(object sender, EventArgs e)
        {
if (!IsPostBack)
            {
	con.Open();
            SqlCommand cmd = new SqlCommand(" SELECT MAX(Id) + 1 as MaxId FROM yourTable",con);

            using (SqlDataReader sdr = cmd.ExecuteReader())
            {
                if (sdr.Read())
                {
                    TxtBox.Text = sdr["MaxId"].ToString();
                   
                }   
               sdr.Close();            
            }
            con.Close();
	}
}

Dear @Joyson,

Please refer above code. it might be helpful.