sum up every 12 months in a table

i have a table calculating the installments. in that table i'm saving all the data recording to that. For example if i'm calculating for 60 installments and saving all the data,so it is like 60 months. so now i need to sum up the value of one column for every 12 months. sometimes v start paying the installments from the middle of the year also.

my DB looks like this.the highlighted column must sum up for every 12 months. two images are one table only. can any one help who to sort

  http://i.stack.imgur.com/pcTfT.png
  http://i.stack.imgur.com/lj9nT.png