Dynamics GP allows an unlimited number of historical and open fiscal years. The following are important guidelines for fiscal years and periods in Dynamics GP:
Each fiscal year can have up to 367 fiscal periods.
Fiscal years cannot overlap.
Each fiscal period within a fiscal year can have a different length.
Fiscal year IDs can only be a four-digit number.
Up to three periods can have the same starting date. This is sometimes, although rarely, used for adjustment periods and is typically not recommended. Best practice is to not have overlapping fiscal periods. If you feel that this will help with your requirements, discuss this with your Dynamics GP resource to determine if this is right for you.
You can make changes to fiscal periods after they have been set up.
You can only post transactions to the last historical (closed) fiscal year. For example, if 2011 and 2012 are closed and 2013 is the first open year, you can still post to 2012, but you cannot post to 2011 anymore...