Small- and medium-sized enterprises (SMEs) represent a significant number of industries in need of moving towards more sustainable development. A sustainability perspective on business activities is today crucial for SMEs to achieve a new level of competitiveness. Identifying which is a suitable set of sustainability indicators for an individual SME is a big challenge. The availability of so many methods and systems can leave SMEs reluctant to implement them in their small business. Therefore, this research aims to create a sustainability maturity model for SMEs to visualize goals and assess progress on their transformation journey. Progress is assessed by indicators, exemplified by indicators of the Global Reporting Initiative and the maturity is verified as stepwise growth along international management system standards. Using the developed model, it is possible to determine the SMEs’ sustainability performance. The research has resulted in a stepwise classification of the organization’s maturity is compiled into training and auditing material in different regions and sectors. © 2024 The Author(s). Business Strategy and the Environment published by ERP Environment and John Wiley & Sons Ltd.