last 12 months data

[#1]

i have two column monthname and consumption value

monthname has the value between aug2010 to jul2012 and also have consumption repectively

now tell me how to calculate consumtion value for the last 12 months

[#2]

Try like:

=sum(if(monthname>=Date( (MonthStart(Today())-365),'MMMYYYY'),consumption))

Regards

R