What is the online safe period calculator? The online safe period calculator is a tool that helps women calculate their safe period. The safe period refers to a period of time when women are less likely to conceive. This period begins on the 5th to 7th day after menstruation and ends 2 days before the next menstruation. Using the online safe period calculator, women can calculate their safe period by entering their menstrual cycle and the date of their last menstrual period. How to use the online safe period calculator? Use the online safety period calculator