a Abstract— Source code copying for reuse (code cloning) is often observed in software implementations. Such code cloning causes difficulty when software functionalities are modified: i.e, cloned codes increase the maintenance cost of software. We aim to estimate the maintenance cost caused by clones. We propose a novel approach, which evaluates influence of cloned codes over the maintenance cost. The basic idea is to measure Functional Redundancy(FR): A degree of propagation of clone-potential functions. FR is measured as follows: First, we cluster functions in the software according to similarities between them. Second, we make n-ary weighted tree(FR tree) based on the cluster. Finally, we measure FR by weight of each node in FR-tree. In this paper, we describe the details of our proposal. We also apply the approach to 17K-ELOC C code to demonstrate its effectiveness. Keywords—FR, Functional Redundancy, Code Cloning, Software Maintenance, Similarity, Cost