January 11, 2021 | 4:16 pm Font Size AAA Flo, a period tracker, is used by more than 153 million women to monitor their menstrual cycle. Screenshot via Flo/flo.health Flo, Calm, and MyFitnessPal are the most popular health apps in the world in 2020, according to the Health App Index from Uswitch, a UK-based comparison website. Half of mobile app users relied on health and fitness apps in order to achieve their fitness goals before the pandemic. That number rose to 75% after the coronavirus disease 2019 (COVID-19) outbreak. The index gathered data from the Apple App Store, search engine optimization company Ahrefs, and analytics company SimilarWeb from December 12 to 20, 2020, to find out the world’s most popular health apps.