The UN Millennium Project (MP) team has conducted a comprehensive cross-country analysis of the interventions and investments required to achieve the Millennium Development Goals (MDGs) .  The MP needs-assessment focuses on a number of pilot developing countries, selected on the basis of their low per capita incomes, geographic and political diversity, and record of sound governance.  In its analysis, the MP team developed a series of spreadsheet-based models that are used to calculate the cost for the interventions required to achieve the MDGs in the pilot countries .  MP methodology is very practical and rich in specific details, but since it relies on exogenous assumptions for economic and demographic growth, it cannot address two issues of interest: (1) the impact of the MDG-related interventions on the economic and demographic development of the country under study and (2) the possible synergies and dissynergies among different MDG interventions.  The work described in this paper  complements and builds on the work of the MP team by addressing these two important issues and evaluating their implications for MDGs costing and financing.  The analysis for this paper was prepared using the Threshold 21 (T21) integrated development model from the Millennium Institute.