I'm wondering how the monthly inflation rate is calculated from the consumer price index?
Here you can find the monthly CPI data from 1913 - 2016: https://fred.stlouisfed.org/series/CPIAUCNS
From this data I want to calculate the inflation like it is presented on this website: http://www.usinflationcalculator.com/inflation/historical-inflation-rates/
I already calculated it by this formula:
((i/l)-1)*100 = inflation rate i = CPI value of the current month l = CPI value from 12 month ago
But I'm wondering if this is correct and if this is the usual way to do it? Wouldn't it better to consider the average inflation of the past 12 month instead of considering just the difference from 12 month ago till current?