Purpose This paper aims to investigate the zakat disclosure of Islamic banks at the global level. It is important for depositors and shareholders of Islamic banks to know whether the bank is paying zakat on their behalf or not. Additionally, disclosing the calculation method used is also necessary to eliminate uncertainties resulting from ambiguous reporting that can mislead the stakeholders. This issue becomes more obvious when considering that depositors and shareholders may have different accounts with different Islamic banks, which makes it quite confusing to have multiple ways of zakat calculation or different approaches on who is the party that pays it. This study analyzes the current practices across 13 countries and recommends best practices. Design/methodology/approach The objective of the paper objective is achieved through analyzing the annual reports of 34 Islamic banks in 13 countries for the years 2014 and 2019. It further quantifies the zakat disclosure by constructing a zakat disclosure index. This index considers the disclosure of four major constituents covering the amount and the responsibility for payment, the calculation method, the involvement of the Shariah board and the zakat duty on investment account holders. For further robustness, this study is further supported by content analysis measures using the zakat word count in annual reports. Findings The results indicate a major issue in zakat disclosure. The overall average of disclosure index is low. Most of the banks disclose limited information about zakat, such as the amount and the responsibility for payment, in their annual reports. Less than 40% of the examined banks disclose information about the role of the Shariah board in zakat calculation, and a very limited number of banks (9%) are found to disclose enough details about the zakat calculation method. Furthermore, none of the examined banks mentions the zakat due for the investment accounts. Overall, zakat disclosure of most of the banks, whether following Accounting and Auditing Organization for Islamic Financial Institutions or otherwise, are found to be not up to the expected best practices. Research limitations/implications Among the limitations of this study is the sole dependence on annual reports of Islamic banks without considering other means that banks might be using to communicate zakat-related matters to stakeholders. Examples of such means include a website, social media and other direct or indirect marketing materials. Additionally, the results of this study shall not be overgeneralized regarding differences between countries because the sample does not include all Islamic banks in the selected country. Future research may use the proposed zakat disclosure index on a country-specific data sample. Practical implications The findings have significant implications as they raise a serious concern regarding the sufficiency of the Islamic banks’ disclosure about a core area of their responsibility, that is, the zakat. The index developed can be a tentative measure of zakat disclosure transparency pending further review. The result further suggests looking at the composition of members of Shariah boards to include at least one member with a sound accounting background. Zakat is a religious duty; therefore, a perceived lack of transparency on the amount, method of calculation and how the zakat is paid may affect the future injection of capital into Islamic banks. Originality/value An important contribution of this paper lies in the fact that the collected data is not provided in any available database. Rather, it is manually captured from the individual annual reports of reviewed Islamic banks. Further, this paper proposes an index to measure the zakat disclosure at bank and country levels.