Progression of nonlinear wave groups to breaking was studied numerically and experimentally. Evolution of such wave group parameters as distance to breaking and modulation depth was described. Numerical model demonstrated a good qualitative agreement with experimental results in describing the behaviour of distance to breaking and modulation depth as functions of initial wave steepnesses. It was shown that energy loss appears to be a function of modulation depth. Energy loss grows with modulation depth up to a certain threshold of the latter.