Definition:
A calendar year, unless provisions of law, a statute or articles of association of the entity keeping the accounting books provide for other (also used for taxation purposes) period which lasts 12 successive full calendar months. In case the entity commenced economic activity in the second half of a calendar year, the accounting books and financial statements of the entity for such the period can be joined with the accounting books and financial statements for the following year. In case of change of the turnover year - the first turnover year after the change should be longer than 12 successive months.

Source:

• Act of 29 September 1994 on Accounting
  Place of publication: (Dz. U. z 2021 r. poz. 217, z późn. zm.)