How do you convert yearly and period CPI to that of a rolling basis?

#1
Hi Guys,

I am doing research and currently I am trying to utilize Consumer Price Index data. I have two sets of consumer price data, one that calculates the change in price from a certain month to that month of last year, and another that calculates the change in price from periods of time.

For example, for the first data set, it allows say, the prices of April 2011 equal to 100. Now it sees how the price of April 2012 has changed and if it is 5%, then it reports the price as 105.

For the second set, it allows the accumulated prices of Janurary to April of 2011 equal to 100. Now it sees how the prices from Janurary to April of 2012 has changed and if it is 5%, it reports 105.

How can I utilize these two datasets to calculate a rolling price data set that I can actually use to compare against other data? Thank you!