Hello Proton Team,

I am writing to request a new feature for Proton Calendar: the ability to set recurring events based on a specific number of days (e.g., "Every 28 days") rather than just "Monthly" or specific calendar dates.

Why this is important: Many users rely on calendars to track health cycles, such as menstruation, which often follow a fixed day count (e.g., 28, 29, or 30 days) rather than a calendar month. Currently, the "Monthly" recurrence option causes the event date to drift over time because months vary in length (28–31 days). This makes the calendar inaccurate for medical or health tracking purposes.

Current Limitation: The only recurrence options available are based on calendar intervals (Weekly, Monthly, Yearly). There is no option to select "Every X days."

Desired Solution: Please add a recurrence option that allows users to specify a fixed interval in days (e.g., "Repeat every 28 days"). This would ensure that health tracking remains accurate regardless of the varying lengths of calendar months.

Thank you for considering this request. Accurate health tracking is a vital use case for privacy-focused calendars like Proton.

Wow thank you for citing peer-reviewed articles Anji - this info was enlightening and health tracking in general seems like it could do a lot of good

Just FYI that drip. is a privacy-respecting period tracker: https://dripapp.org/

From their privacy policy: "There is no collection of usage data or personal information, no ads, no spyware. Drip can store data related to menstrual health locally on your device."

I also wanted to point out that adding this type of tracking functionality could be used for tracking other things as well. For example mood tracking, meditation practice tracking, exercise routine, taking medication, etc. It would be extremely useful for a large number of people.

In today's socio-political environment many women are in danger of having their menstrual tracking data used to jail or kill them for "crimes" such as using birthcontrol or having a miscarriage. Having this data in a secure encrypted place will save lives. If menstruation specific events / data tracking could be added to the calendar it would be extremely helpful.

Expanding Privacy Services
Proton can extend its privacy-focused offerings (email, cloud storage, VPN) by adding an encrypted period tracker, reinforcing its commitment to user security.

Addressing Privacy Concerns
With growing data privacy awareness, users need secure options for sensitive health data like menstrual cycles. An encrypted tracker ensures this data remains private.

Future-Proofing
As demand for secure health tracking rises, an encrypted period tracker will keep Proton ahead in the privacy tech landscape.

here are some peer-reviewed articles on why this is important, and why Proton, a provider of privacy-oriented solutions, should get into this market.

“Period-tracking apps are part of a fast-growing FemTech business industry, with an estimated current market value worth upwards of $60 billion. Recently, however, the data and privacy around this revolutionary tool have justifiably been called into question in a post-Roe America. […] FemTech companies can help ensure period-tracking apps are utilised to safeguard the bodily autonomy of users and not to be used as a weapon against them.” Missed period? The significance of period-tracking applications in a post-Roe America, Kelly & Habib 2023 https://www.tandfonline.com/doi/full/10.1080/26410397.2023.2238940#d1e245

“The menstrual cycle is considered a biological marker that predicts women’s general health [...] Moreover, mobile app use was reported to enhance [positively] the outcomes of several chronic illnesses and health issues” Smartphone Applications for Period Tracking: Rating and Behavioral Change among Women Users, Karasneh et al 2020 https://onlinelibrary.wiley.com/doi/10.1155/2020/2192387

“Femtech is the use of digital technology for women's health. It is expected to grow at a compound annual growth rate of 16.2% from 2021 to 2027 […] There is an ever-increasing need for technology to support people who menstruate as not only physiology, but also socioeconomic, religious and cultural factors can influence people's experiences of menstruation, meaning that not all menstrual cycles are universally similar. […] The main reason for using a period tracker app is for users to track their periods, with the second most common reason being to avoid pregnancy. However, there is a range of other possible benefits from using the apps, from the empowerment of menstrual health to mental health.” Experiences of users of period tracking apps: which app, frequency of use, data input and output and attitudes, Patel et al 2024, https://www.rbmojournal.com/article/S1472-6483(23)00698-3/fulltext
https://onlinelibrary.wiley.com/doi/10.1155/2020/2192387