The gray economy is actions that are performed within the unofficial economy, ie they contribute to the gross domestic product, but are not legally registered or are semi-registered. One of the biggest causes of the gray economy is considered to be the excessive tax burden, so in Croatia the largest part of the gray economy refers to "undeclared work", ie undeclared work and non-fiscalization of accounts. According to the latest data, the gray economy in Croatia accounts for 28% of total GDP or 13 billion euros, which ranks it at the very top in terms of the share of the gray economy in the European Union. The highest percentage of the gray economy occurs in sectors that use cash transactions, such as the provision of household services, repair services and sports services. By joining the EU, Croatia had to include the gray economy in the calculation of GDP, and by including the gray economy, meeting the Master Criteria has not changed. Eurostat has developed an Exhaustiveness program for candidate countries to achieve better comparability. Croatia was not included in the program, but following the example of Eurostat's program, it included a correction for the gray economy in its official GDP, which enabled it a more realistic view of development. There are several methods of calculating the gray economy, but none can determine the exact volume. Detailed research on the gray economy is based on scientific papers from previous years and is not representative today. In Croatia, a minor reform in combating the gray economy was adopted in 2013. The reform has changed and improved over the years, and the latest change was introduced on April 1.2020, according to which every previously issued document and final invoice will have to be fiscalized. Also from 1.1.2021. year taxpayers must have a QR code for easier and faster verification of accounts.