This dissertation presents a methodology of short-cutting the phosphorus (P) cycle in urban ecosystems. In nature the P-cycle is a circular, closed loop system, but human activities use and dispose P in a linear, open-ended system leading to familiar environmental problems. Lake Chivero in Zimbabwe is used as a case study to illustrate the unsustainable practice of discharging valuable and finite P resource into water bodies used as drinking water sources. Short-cutting or closing the P-cycle in the urban environment is closely related to closing of water cycles. Closing the P-cycle is dependent on the adoption of ecological sanitation and eco-city concepts. These concepts bring forth solutions, which are source orientated (local and small scale), non-mixing, ecologically sound, closed loop systems. Recycling of P in urban ecological agriculture (without synthetic fertilisers) is used in this dissertation to test the feasibility of these concepts. A phosphorus calculator has been developed, based on studies of monthly P-fluxes and stocks in a high-density suburb extending over 6.5 Mm2 in Harare, Zimbabwe, where agriculture is already a major activity. The P-calculator is a model based on STELLA, a system's analysis software developed by High Performance Systems Inc. The mathematical formulations derived for P-fluxes and stocks are based on observations and literature. The calculator provides a means to simulate and evaluate different scenarios in linking household waste P-fluxes to agricultural P-requirements using environmental sustainability indicators.