This article presents a method to fast estimate the development effort of Web-based information systems in Chile. The method, called Chilean Web Application Development Effort Estimation (CWADEE), addresses a necessity to get effort estimations in a short period of 24 to 72 hours using limited information. In contrast with other existing methods, CWADEE uses raw historical information about development capability and high granularity information about the system to be developed, in order to carry out such estimations. This method is simple and specially suited for small or medium-size Web-based information systems. CWADEE has been applied to twenty-two projects with very accurate results.