This paper explores how different theoretical viewpoints on market integration and socioinstitutional settings alter farm viability assessments based on (semi)subsistence farm income measurements. The measurement of net farm income (NFI) is presented under two approaches: one based on Neoclassical Economics, and another from a Neo-Institutional perspective. Using data from Sierra Leone it is demonstrated that the assumptions about (output and input) market integration/participation, labour usage accounting and other institutional arrangements of (semi)subsistence farming affect NFI calculations. As a consequence, different farm viability readings emerge, directly influencing the outcome of policy decisions.