The daily recording of basal body temperature is the most useful method of determining the term of ovulation by resolving the rise in temperature. To support this aim, Graphical User Interface (GUI) system is designed and implemented to visualize the basal body temperature variations on daily basis by using android platform smartphone with programming multi-thread Java modules. To estimate the occurrence of ovulation cycle, a new method of analyzing the low-frequency features including a DC level and the second largest peak in frequency spectrum domain is proposed with interpreting the prominent features into the average basal-body temperature variations and a menstrual cycle.