Per month : 

  1st month ( 01/01 - 31/01 ) until 31/03
  2nd month ( 01/02 - 28/02 ) until 30/04
  3rd month ( 01/03 - 31/03) until 31/05
  4th month ( 01/04 - 30/04) until 30/06
  5th month ( 01/05 - 31/05) until 31/07
  6th month ( 01/06 έως 30/06) until 31/08
  7th month ( 01/07 έως 31/07 ) until 30/09
  8th month ( 01/08 έως 31/08) until 31/10
  9th month ( 01/09 έως 30/09) until 30/11
10th month ( 01/10 - 31/10) until 31/12
11th month ( 01/11 - 30/11 ) until 31/01
12th month ( 01/12 - 31/12 )until 28/02