Variable offset on calendar month

Hello Experts -

I need to display all the months in a year. And then have a YTD column and a Last Year-to-Date column.

My user prompt is the calendar month. How can I use this to display all the months in that year?

I know about variable offset but if the user enters May 2008, then -1 would give me Apr 2008. I need to start from Jan 2008.

Any suggestions any one please?