Your Period Data Should Be Private

The data we keep on our phones is sensitive. For women, period data is one of the most sensitive data points we share with our device.

That’s because period tracking apps aren’t just about when your period happens. Apps in this space ask you to log extremely intimate details so it can predict your cycle or help you get pregnant. From when you bleed, but also when you've had that late-night chocolate craving, and even when you have a miscarriage.

In the Post-Dobbs landscape, we believe safeguarding this data and keeping it private is more important than ever. Our privacy expert Shoshana Wodinsky did hands-on testing of 6 popular period tracking apps: Euki, Clue, Flo, Period Calendar, Planned Parenthood’s Spot On, and Stardust. We discovered data sharing to analytics companies, privacy-washing, but also, a stand-out option when it comes to keeping data safe.

For this investigation, we partnered with Transparency Hub at Harvard's Berkman Klein Center to examine historical changes to these apps' privacy policies. The Siebel School of Computing and Data Science at the University of Illinois provided additional Android testing.

We tested:

1. Euki, a privacy-first tracker and open-source project managed by the Euki non-profit (10/10)
2. Clue, a clinically-minded tracker based in Germany (8/10)
3. Flo, a data-hungry tracker with an AI symptom chatbot (7/10)
4. Period Calendar, the only ad-supported app we tested (6/10)
5. Spot On, Planned Parenthood's cycle and birth control tracker (5/10)
6. Stardust, an astrology-themed tracker popular with younger users (2/10)

Here are the 4 things to know:

• Using a period tracker isn’t neutral information

If your period tracker broadcasts to advertisers that you’re using a period app, that persistent identifier is folded into your ad profile. The next time an ad follows you around the internet, your reproductive health becomes part of the calculus.

• Watch out for the in-app browser

When you open a page in an app’s browser, you're often no longer inside a privacy-protective app. Core tracking might be locked down tightly, but the moment you enter the web layer, third-party trackers wake up and start collecting data, including details you'd expect to stay private.

• Safety and Privacy are sometimes just marketing

The app Stardust once marketed itself as an "encrypted," privacy-safe sanctuary in the wake of Roe. Reporters later found that it offered standard encryption rather than the end-to-end protection the language implied, and the company quietly removed the claim.

• Choosing a private app does matter

We all deserve the option to use technology for women’s health. Sometimes, this desire is exploited by flawed designs around privacy. For some of the apps we tested, a lot of the protection falls on you. Is this unpaid labor just the unwritten cost of owning a smartphone? Or another chore women don’t have time for?

We don’t need tech creeping into our mental load. We recommend using Euki. The app earned a perfect score for a refreshingly simple reason: there's almost nothing to leak. Euki keeps your data on your phone.

Your period is private. Make sure your app agrees.