In years gone by, women would rely on the calendar on the wall to work out when their next menstrual cycle might occur. They would look to physical signs to tell them when they might be ovulating, and therefore when they’d be most likely to fall pregnant. More recently, we’ve seen the proliferation of mobile phone applications helping women track their current cycle, predict their next cycle, and work out when the best time is to try for a baby. There are more than 400 fertility apps available, and over 100 million women worldwide are using them. The personalisation and convenience of apps makes them empowering and attractive. But they require some caution in their use.