[ecfisa]

Hola oscjae.

Un ejemplo de como podes implementar lo que solicitas:

Código Delphi [-]
...
procedure TForm1.FormCreate( Sender: TObject );
var
  i: Integer;
  Field: TField;
begin
  with tu_DataSet do
  begin
    Close;
    SQL.Text :=  'SELECT CAMPO1, CAMPO2, ... FROM TU_TABLA';
    Open;
  end;

  tu_DataSet.Close;

  for i :=0 to tu_DataSet.FieldDefs.Count - 1 do
    Field := tu_DataSet.FieldDefs[i].CreateField( tu_DataSet );

  Field := TFloatField.Create( tu_DataSet );
  with Field do
  begin
    FieldName  := 'CalcFld';
    Calculated := True;
    DataSet    := tu_DataSet;
  end;

  tu_DataSet.Open;
end;

procedure TForm1.tu_DataSetCalcFields( DataSet: TDataSet );
begin
  with DataSet do
  begin
    FieldByName('CalcFld').AsFloat := PI * ( Fields[0].Value + Fields[1].Value );
    //...
  end;
end;

Saludos