Period over Period in a table


I'm attempting to do a Period over Period in a table, but want to keep the date range to previous week/month/quarter to keep it auto-updating and grouping the data in a particular way. My idea was to create a new column in ETL that is the same as the column I'm trying to do a Period over Period calculation, but from the previous years value. Then I can make the Period over Period calculation myself in Beast Mode. I'm having trouble doing this in the ETL does anyone know how to perform this? Or another solution to this problem?