One of the major challenges of the profile extrusion process is to obtain a homogeneous melt flow distribution at the die outlet, i.e., a balanced flow. The geometric complexity of the profiles to be extruded, along with the rheological properties of the polymer melt and their dependence on shear rate and temperature, complicates the die design process. In order to obtain an adequate flow distribution at the die exit, the flow channel geometry must have a specific design. In most cases this encompasses an experimental trial-and-error procedure, which consumes a huge amount of time and resources, and relies utterly on the designer’s experience. The large number of works on computer aided die design clearly indicates the ability to accurately predict and adjust the fluid flow distribution using numerical tools. These tools are a better alternative for the usual experimental trial-and-error approach, with the advantage of reducing the cost and resources involved during the required trials. However, there is a limited number of industrial die designers that can have access to numerical tools. Considering these facts, it is of significant importance to provide those with simplified die design guidelines. In this work, numerical modelling tools were employed to devise analytical equations to balance the flow in T and L shaped extrusion dies. The two modular geometries, T and L, where chosen since the majority of the complex profiles can be built through their combination. The above referred equations establish relationships between the parallel zone lengths and the thicknesses of the different sections composing these dies, with a view to obtain a balanced flow distribution. A design methodology was proposed for complex geometry dies (composed by several L and T modules) to guide the die designer through a series of steps/calculations needed to define all the parallel zones lengths. The usefulness of the proposed methodology is illustrated in a number of case studies.