The present invention discloses a device and a method to predict fertile window of a female human accurately by 98.9% by tracking the fertile and infertile days of her menstrual cycles thereby facilitating planning or prevention of pregnancy. For the purpose, the present involves analyzing user™s skin temperature and change in resting heart rate recorded at regular time intervals. The device of the invention is preferably a wearable device comprising: a temperature sensor measuring the skin temperature, an optical sensor recording the resting heart rate, a controller used to process the data obtained from the temperature sensor and optical sensor to predict the fertility window accurately for a female human. The results are then transmitted to a cloud based memory cell. The obtained data i.e. the skin temperature and change in resting heart rate is collected for a particular user over a period of multiple menstrual cycles. Figure 3.
