Abstract Eco-city planning has been a prevailing concern throughout China and beyond over the past few decades. Least-cost planning is a life-cycle costing approach for alternative analysis and decision-making, determining the preferred option that provides the optimal mix of financial, social and environmental outcomes for stakeholders throughout the project lifespan. A more sustainable approach is to incorporate the low carbon context into this economic analysis. Case studies, Tianjin Eco-city and Ningbo-Cixi Wetland Centre, granted by GEF, are presented and reviewed on how to foster key coastal areas of China into eco-cities by means of carbon footprint and costing. It is demonstrated that consideration should include carbon impact, carbon costs and accounting processes in the planning and management of the relevant plots, with achievement of key performance indicators relating to greenhouse gasses. Tertiary wastewater treatment, the selection of low carbon emission technology, and the utilization of constructed wetland configurations, green buildings and facilities are particularly demonstrated and modelled, employing energy software and economics tools repectively.