There is limited evidence-based data on income-generating interventions, both within thehumanitarian and the development field. Nevertheless, there is a growing and unavoidable nexus between the two fields, and therefore also, within their methodologies for measuring project intervention results, as well as their success rates. The challenge in many cases,however, is finding a measuring system which does not only account for a project’s expenditures, but can also tell something about a project’s effectiveness, which can then be compared to similar intervention’s results, and applied in future endeavors. Hence, this study analyzes the economic effectiveness of an Income Generating Activity (IGA) project in rural Guatemala as a case study, using an Economic Rate of Return (ERR) as the basis of measurement, which is acquired using a cost-benefit analysis (CBA). The study draws on the various viewpoints of scholars on the subject, taking into account different Monitoring and Evaluation (M & E) practices, particularly in the manners carried out by the United Nations and the World Bank, as they have long histories of M & E practices in the field. It especially lays emphasis on the Sustainable Livelihoods Framework (SLF), which is a tool which is often used within humanitarian work as well as in development to determine possible economic opportunities in communities. Although the study aims at IGA programs in the humanitarian sector, data within development projects is also explored in this thesis, because longer timeframes within development, allow for more careful study of long-term results, which is usually a requirement for the evaluation of livelihood. Results within the development sector allow for more careful study of results, and more certain conclusions than within the humanitarian sector, which due to its emergency settings, usually has a more difficult time collecting data.This study then makes an ex-ante analysis of the case study in question, which is a potential aquaponic fish tank project, with economic benefits, in the unattended, post-disaster settings of San Andrés Osuna, Guatemala, following the eruption of the Volcan de Fuego, in 2018. The study reveals that the project has a potential ERR of 280 percent, compared to other WorldBank projects which tend to have an ERR ranging between 15 and 25 percent. Nevertheless, other projects which have also been explored by this study, also offer results ranging ERRs of about 280 percent as well. Many times, projects utilize cost-efficiency analysis which make them more difficult tocompare and contrast to other projects than if they had used ERR results, to measure the projects’ success. This comparison of projects can help decision makers better allocate their resources to the most efficient income generating projects in the future, which can therefore better economic livelihoods of people in post-disaster settings. The World Bank has used this ERR as an indicator for their cost-benefit analyses for the past 70 years, but is increasingly utilizing it less and less, whilst other humanitarian and financial organizations, do not use it at all; making this a possible issue within the field.