Technical Abstract: Pasture management in tropical agro-ecosystems is challenging because of unique soil, climate, and animal interactions. Budgeting forage as part of the grazing system can be difficult because of the strong seasonality of forage production and rapidly changing forage quality. Planning, measuring, and budgeting the forage supply will help the farmer decide if there will be adequate forage for grazing animals to meet performance goals. Quantifying and describing the forage resource will also better equip the farmer to cope with shortages of forage as well as excess forage in certain times of the year. Knowledge of the amount and distribution of the forage resource available during the year will facilitate timely decision making to achieve pasture and animal performance goals and improve overall forage, pasture, and animal management an important consideration for integrated crop and livestock systems. Quantitative management of the forage resource, however, requires accurate measurements of forage supply and demand. In this paper, we will (1) discuss the relationships between grazing animal demand for forage and the herbage supply on pasture, (2) describe the tools available to farmers for measuring herbage mass in pastures, and (3) illustrate how to construct a forage budget by integrating these items to meet the nutrient needs of grazing livestock during the year. We will draw on examples of research and experience regarding forage budgeting for grazing systems, principally dairy, in temperate regions of the world and try to adapt the basic principles for the tropical grazing agro-ecosystems of Brazil.