Create a New Fiscal Period in Dynamics GP

Go to: Tools>>Setup>>Company>>Fiscal Periods

Where it says Year overwrite the year with the new year.

This should set up your first and last day of new year, if not then in the First Day field, type in the first day of the fiscal year and in the Last Day field, type in the last day of the fiscal year.

Your Number of Periods should be 12.

Hit Calculate and you will get the following screen: