The pressure in an impacting liquid drop against both a rigid and an elastic target is calculated for the period when the contact region is expanding faster than the wave speed in the liquid. For very low speed impact a geometrical-acoustics model is shown to give a good representation of the solution, until the edge speed approaches the wave speed. A self-similar solution, that takes account of nonlinear effects, is used in the neighborhood of the contact edge. Comparisons are made with linear theory and numerical calculations.