Here is a list of some common mistakes that companies make when calculating and disclosing earnings per share (EPS) under IAS 33, and how these can be avoided:

1. Incorrect identification of potentially dilutive securities: One of the most common mistakes is the incorrect identification of potentially dilutive securities that could impact the calculation of diluted EPS. To avoid this, companies should carefully review their financial statements and notes to identify all potentially dilutive securities and ensure that they are included in the calculation of diluted EPS.
2. Incorrect calculation of the impact of potentially dilutive securities: Another common mistake is the incorrect calculation of the impact of potentially dilutive securities on diluted EPS. To avoid this, companies should carefully review the terms and conditions of all potentially dilutive securities and use appropriate models or software to accurately calculate their impact on diluted EPS.
3. Failure to adjust for changes in potentially dilutive securities: Companies may also fail to adjust the calculation of diluted EPS for changes in potentially dilutive securities that occur during the period. To avoid this, companies should carefully track changes in their potentially dilutive securities and adjust their calculation of diluted EPS accordingly.
4. Inconsistent treatment of potentially dilutive securities: Companies may also make mistakes by inconsistently treating potentially dilutive securities from period to period or across different types of securities. To avoid this, companies should establish clear policies and procedures for the treatment of potentially dilutive securities and apply them consistently.
5. Incorrect calculation of weighted average number of shares: Another common mistake is the incorrect calculation of the weighted average number of shares outstanding, which is used in the calculation of basic and diluted EPS. To avoid this, companies should carefully track the number of shares outstanding and the dates on which they were issued or repurchased.
6. Lack of transparency in disclosures: Companies may fail to provide sufficient transparency in their disclosures related to EPS, including the assumptions and methods used to calculate basic and diluted EPS. To avoid this, companies should provide clear and detailed disclosures that allow investors to understand how EPS was calculated.

Overall, companies can avoid these common mistakes by establishing clear policies and procedures for calculating and disclosing EPS, carefully tracking changes in potentially dilutive securities, using appropriate models or software, and providing transparent and detailed disclosures to investors.