How to estimate the daily growth of a tablespace: 

select
   dhs.begin_interval_time,
   dt.tablespace_name,
   trunc(dhtsu.tablespace_size*dt.block_size/1024/1024/1024)  gb,
   trunc(dhtsu.tablespace_usedsize*dt.block_size/1024/1024/1024) gb_used
from
   dba_hist_tbspc_space_usage dhtsu,
   v$tablespace vts,
   dba_tablespaces dt,
   dba_hist_snapshot dhs
where dhtsu.snap_id = dhs.snap_id
and   dhtsu.tablespace_id = vts.ts#
and   vts.name          = dt.tablespace_name
and vts.name                         = '&tablespace name'
order by 2,1 desc;