Abstract Dairy farmers in the northern irrigation region of Victoria (NIRV) in Australia predominantly produce milk from flood irrigated pastures, although increasing amounts of concentrate and forage supplements are being incorporated into lactating cow diets to increase their milk production. The competitive advantage of the irrigated dairy industry has been the low cost of production, but total productivity gains over the last 20 years have only been about 1.3%. While some farmers have made substantial productivity gains through improved pasture utilisation and effective use of supplements, others have combined these feeds inefficiently. There is a role for decision support tools to assist farmers in making both strategic and tactical feeding decisions to feed their herd as efficiently as possible. This paper reports on a simple tactical decision support tool, ‘Diet Check’, developed to help dairy farmers in the NIRV estimate whether their cows are consuming sufficient metabolisable energy (ME), crude protein (CP) and neutral detergent fibre (NDF) for a specified level of milk production. Diet Check has a unique method of estimating pasture intake and nutrient intake from pasture, as well as substitution of supplements for pasture, and is useful when cows consume more than 50% of their total energy intake from pasture in strip-grazing or small paddock rotation systems. Model inputs can be determined on-farm, and it allows the user to test the effects of different feeding and herd management scenarios before applying them. It has provided a means of packaging local research results into a practical and user-friendly tactical decision support tool and, also provides a valuable learning tool used in extension activities.