Estimating time and costs is a crucial factor in application development projects and low error margins are a priority.

In line with the very fast evolution of Internet technologies, all applications are quickly becoming Web Applications, which are growing without a consolidated project methodology.

Thus there is a clear need for an estimation model for these applications' development projects.

The aim of the present paper is to illustrate a new Web Application cost estimation model that can form the starting point for any development project.

The estimation model described in this paper is called MMWA (Metrics Model for Web Applications). This is an "early measures model", since the measurements are effected at the start of the software life cycle, with a view to accurately estimate time and costs so that the right decisions can be taken concerning the development of the Web Application in hand.