Adjacency between vertices, degree of the vertices and distance between every pair of vertices are the graph properties used in the calculation of molecular topological index. More the number of properties, the calculation complexity increases. In this paper we propose a method of determining the molecular topological index of trees with equal number of vertices of a given degree from triangular matrices. Also determining the molecular topological index of such trees from its subtree is also determined. © Published under licence by IOP Publishing Ltd.