With the adoption of the 2030 Agenda for Sustainable Development, the United Nations Member States pledged to reduce inequality in all its forms through Sustainable Development Goal 10, while ensuring that “no one will be left behind.” This paper proposes a methodology that governments and stakeholders can use in their countries to measure inequality of opportunity, using data from nationally representative household surveys. The Dissimilarity Index (D-index) allows a comparison of inequality of opportunity levels among countries. The paper also proposes an innovative approach, the classification and regression tree (CART) analysis, to identify households and individuals furthest behind in access to basic opportunities in the Asia-Pacific region. Regression trees offer a practical way of operationalizing the pledge to leave no one behind (LNOB), accelerating national progress to achieve the Sustainable Development Goals (SDGs).