A field experiment was conducted to work out relationship between heat unit requirement and phenophases of two wheat cultivars (PBW-343 and WH-542 ) under different dates of sowing (2 November , 1 December and 4 January). Growth duration and heat unit requirement of different phenophases was distinct for two cultivars, and showed a decline with delay in sowing. High temperature during reproductive development in late-sown crop forced the plants to attain maturity. For all phenological stages, plants of timely-sown crop accumulated more heat units in both cultivars than late-sown crop. The pheno-thermal indices decreased during vegetative stages but increased during reproductive phenophase with delay in sowing. The cultivar, PBW-343 took more number of days, accumulated more heat units and used heat more efficiently; and thus produced higher grain yield than WH-542. The timely-sown crop used heat more efficiently and yielded higher than late-sown crop. It was concluded that timely- sown crop exhibited best growth and grain yield as the favorable environmental conditions coincided with heat unit requirement of different phenophases of wheat.