Magnetic Random Access Memory (MRAM) is a non-volatile memory which is widely studied for its high speed, high density, small cell size, and almost unlimited endurance. However, for deep-submicron process technologies, significant variation in MRAM cells' operating regions results in write failures in cells and reduces the production yield. Currently, memory designers characterize failed MRAM chips to find a suitable current level for reconfiguring their operating current, which is timeconsuming. In this paper, we propose an efficient operating current search method and a built-in circuit for toggle MRAM, which can rapidly find a customized operating current for each MRAM chip. With the built-in circuit, an MRAM chip can dynamically reconfigure its operating current automatically. Production yield and product life-time thus can be increased.