Read
- Developer of Popular Women’s Fertility-Tracking App Settles FTC Allegations that It Misled Consumers About the Disclosure of their Health Data;
- Lawsuit claiming Flo Health app shared intimate data with Facebook greenlit as Canadian class action;
- Google, Flo Health to pay $56 million in period-tracking app privacy case;
- Menstrual tracking app data is a ‘gold mine’ for advertisers that risks women’s safety;
- You Give Apps Sensitive Personal Information. Then They Tell Facebook
Android:
iOS:


PrivacyGuides has a section about this on their website: https://www.privacyguides.org/en/health-and-wellness/#menstrual-cycle-tracking
At the time of writing, it seems Drip is the best option on both iOS and Android. The app is free, open-source, and all data is completely local. Honorable mention to Euki as well