Formation of the first bubble at nucleation site is an inception of the two phase flow in pool boiling and flow boiling. Bubble dynamics (bubble nucleation, growth, and departure) plays an important role in heat transfer and pressure drop characteristics during two phase flow in microchannels. In this paper, a simplified model has been developed for predicting bubble growth rate at nucleation cavity in microchannel. It is assumed that heat supplied at nucleation site is divided between the liquid phase and the vapor phase as per instantaneous void fraction value. The energy consumed by the vapor phase is utilized in bubble growth and overcoming resistive effects; surface tension, inertia, shear, gravity, and change in momentum due to evaporation. Proposed model shows a good agreement with available experimental works. In addition, the bubble waiting time phenomenon for flow boiling is also addressed using proposed model. Waiting time predicted by the model is also close to that obtained from experimental data.