A novel approach to address the disco planning issues in a competitive electricity market environment is presented in this paper. Since there exists a variety of electricity markets and associated products and services (i.e. energy markets, ancillary service markets, etc.) which work in different time-frames, the mathematical model presented here uses the AC power flow, and the planning problem is a dynamic model, formulated to tackle all these issues simultaneously. The effects of DG injections on the distribution network, both in the short-term operations (impact on losses) and in long-term planning (impact on feeder capacity) is combined together and mathematically formulated within a comprehensive objective function for planning. Novel goodness factors accounting for DG contribution to system loss reductions and deferment in feeder capacity upgrades are formulated as monetary values.