Abstract: With the advancement of technology, mobile devices nowadays incorporate multiple Radio Access Technologies (RAT). So, switching from one RAT to another becomes obvious. This procedure is called vertical handover. Universal Mobile Telecommunication System (UMTS) and Wireless Local Area Network (WLAN) are two such networks whose interoperability is being studied for years. WLAN covers relatively smaller area but provides a high data rate, on the other hand, UMTS covers a larger area but has comparatively lower data rates. We know heavy load on a particular cell can deteriorate its performance. Therefore, both the networks can co-ordinate to facilitate each other if loads of their neighboring cells are quite high. In this work we propose a dynamic load balancing heuristics using adaptive handover thresholds, which adapts as per the traffic load in a given cell. This can improve the service provided to the end users who are at the edge of the cell or closer. The metrics for performance considered in this work are outage probability and handover area.