The taxpayers who have registered their economic operation before 13 October 2015 are obliged to submit information on main economic activity for the previous tax year in the Electronic Declaration System of the State Revenue Service until 1 May 2016. The core economic activity is considered for the largest share of total revenue of the previous fiscal year if it has been revised or does not comply with the information submitted previously.

NACE Classification of Economic Activities is available in the website of Central Statistical Bureau 

The taxpayers who commence economic activity should indicate the core activity during registration or within one month following the registration. The core activity is determined by tax payer on the basis of planned revenue figures.