Evaluation of accumulated knowledge level for a student is a critical aspect in any learning program and therefore in an e-Learning system. Proper estimation of accumulated knowledge may bring valuable information regarding the student and the effort that he needs to have in order to achieve certain goals. On the other hand, proper estimation can bring very useful information about e-Learning system efficiency. In this context this paper presents a procedure of estimating student's accumulated knowledge based on concept maps. The procedure computes the percentage of covered concepts for a discipline that is partitioned in chapters.