How to Find out database growth in a year

SQL> select to_char(creation_time, 'RRRR Month') "Month",
sum(bytes)/1024/1024
"Growth in Meg"
from sys.v_$datafile
where creation_time > SYSDATE-365
group by to_char(creation_time, 'RRRR Month'); 
Month                            Growth in Meg
-------------------------------- -------------
2010 August                              18760
2010 December                            16200
2010 July                                36600
2010 November                            29740
2010 October                             10800
2010 September                            8900
2011 April                               12160
2011 February                            39500
2011 January                             18000
2011 June                                 1740
2011 March                               10800

Month                            Growth in Meg
-------------------------------- -------------
2011 May                             37808.875

12 rows selected.

SQL>