This study examines how food prices and related seasonality factors affect the dietary choices of low-income farm households in rural Tanzania. The Kishapu and Mvomero districts were selected based on contrasting rainfall patterns, farming practices and economic activities. Data were collected before and after harvest in 2014, using household surveys, focus group discussions, key informant interviews and monthly market-price surveys. A linear-programming solution provides a choice-diet bundle of food items, given model constraints. The cost of the choice diet was compared with household incomes to determine diet affordability. Cheaper, more energy-dense foods lacking other nutrients were consumed at lower budgets in both seasons. Policies and strategies to address problems of the high cost of nutritious foods should be considered to enable low-income households to consume affordable but nutritious diets. Moreover, strategies and interventions that can influence behaviour and promote awareness are important for better household nutrition through a suitably balanced diet of available foods.