A field investigation was carried out to study the influence of irrigation on phenology and accumulated heat units of four cultivars of bread wheat (Triticum aestivum L.) at different phenological stages over two growing seasons. There were three treatments: rainfed, 10 and 20 mm irrigation. The rainfed plants had significantly shorter phenological stages and lower growing day degree than the irrigated plants in all the four cultivars. Cultivars Akbar was found to be early and C 306 was found to be late maturing. Akbar had the lowest and C 306 had the highest growing degree days during all the phenological stages under each irrigation regime. Heliothermal units also showed more or less the same trends. The phenothermal indices and heat use efficiency were found to be higher in the irrigated plants than the rainfed plants.