Traditional software development approaches is obsoleting day by day and the place is being taken by some new evolved approaches like. Cleanroom development approach, Agile development approach etc. due to the evolution in development methodology there is a strong need of evolution in estimation models also. In this work we have proposed an extended version of COCOMO that is E-COCOMO and based on this model a tool has been implemented called OpenECOCOMO. The evolved model is proposed for the new development methodologies and includes some more factors for estimation used in these new approaches.