Period & Fertility Tracking Apps: How Safe Is Your Data?

Millions of women use fertility and period tracking apps every day. Some just want a simple reminder of when their next period is due. Others rely on them to plan or avoid pregnancy, keep track of symptoms, or stay on top of their health. What began as a niche tool has become one of the most personal spaces in digital life — a place to log moods, intimacy, and physical changes that many people wouldn’t share anywhere else.

This growth is part of a booming FemTech industry. In 2023, the global market for female health technology was valued at nearly 52 billion U.S. dollars, with forecasts suggesting it could more than double by 2029. Period and fertility trackers are a big piece of that puzzle, with more than 50 million women worldwide estimated to use them.

In the U.K., 38% of women report using these apps, primarily to track their menstrual cycle, while nearly one-third of women in the U.S. track their cycles, symptoms, or fertility windows digitally. After the Dobbs decision overturned Roe v. Wade, studies even found an increase in tracker use across several U.S. states.

Period apps promise empowerment through knowledge by helping women prepare for upcoming periods, spot patterns, have better conversations with healthcare providers, and make informed choices about family planning. But alongside that empowerment comes a difficult question: where does all this sensitive data go once it’s logged?

Because here’s the catch: from the moment you start entering details, your cycle, moods, sexual activity, and lifestyle choices may be collected, stored, and sometimes shared.

What Do Period and Fertility Apps Really Track About You?

What makes these apps so powerful is also what makes them sensitive: they don’t just track dates, they gather details that map out some of the most personal parts of your life.

The start and end of each period, which, over time, build a clear record of your cycle length and patterns.

Predictions for ovulation and fertility windows, often based on algorithms that get more accurate the more you log.
Daily symptoms like cramps, headaches, bloating, or skin changes.
Notes on sexual activity, contraception use, or whether you’re trying to get pregnant.
Lifestyle details such as mood swings, sleep quality, exercise, or weight.
Pregnancy test results, miscarriages, or other reproductive health events.
Put together, this creates a detailed timeline of your health, your habits, relationships, and even your plans for the future.

Top 5 Period & Fertility Tracking Apps Millions of Women Use

A few apps dominate the fertility and period tracking space, each with millions of downloads and active users. Here’s what you should know about the biggest names:

Flo

With more than 380 million downloads worldwide and around 70 million monthly active users, Flo is one of the most widely used period trackers. It offers predictions, pregnancy tracking, symptom logging, and health content. In 2021, the FTC found it had shared sensitive health data with Facebook and Google for marketing purposes despite promising not to. Today, Flo emphasizes stricter privacy controls, but it still collects detailed health logs, device data, and app usage patterns.

Clue

Based in Berlin, Clue has over 15 million users and markets itself as a science-based alternative. It’s CE-marked as a Class 1 medical device in the EU, which sets it apart from most other trackers. Clue lets users log periods, symptoms, moods, and sexual activity, while claiming strong privacy protections and a commitment not to sell personal data. Still, it collects cycle data, device information, and app analytics, storing most of this on its servers.

Period Tracker / Period Calendar

Sometimes just called “Period Tracker,” this app has more than 300 million users worldwide. Its strength is simplicity: calendar-style tracking that appeals to people who want straightforward predictions and reminders. It collects standard cycle logs, sexual activity, and symptoms, along with device and usage data. Because of its size and less prominent public stance on privacy, critics warn that users should read its data policies carefully.

Glow

Glow focuses heavily on fertility and conception, though it also offers general reproductive health tracking. Across its ecosystem of apps and communities, it has around 25 million users. Glow collects period and fertility data, sexual activity, pregnancy test results, and lifestyle details. It also connects users to forums and partners, which can create additional data-sharing risks. Glow has been criticized in the past for how it handled sensitive data, thoughthe company has since updated its privacy policy.

Stardust

A newer entrant that shot to fame after the Dobbs decision in the U.S., Stardust mixes astrology with science, appealing to younger users who like its lunar cycle themes. Stardust brands itself as privacy-first and says it encrypts health data, separating identity information from cycle logs. But investigations found earlier versions shared phone numbers and device metadata with analytics firms, and its policy once allowed data sharing with law enforcement even without a warrant. Today, Stardust says it only complies with legal requests.

The Hidden Privacy Risks of Period Tracking Apps

The biggest risk isn’t what you type in, but what happens once that data leaves your phone. Some apps store logs locally, but many upload them to servers where the information can move far beyond your control. From there, it may be:

Shared with advertisers or analytics companies looking to profile users.
Sold for marketing — for example, targeting you with ads for pregnancy tests, supplements, or baby gear.
Requested by insurers or even employers under certain circumstances.
Exposed in a data breach if the app’s security isn’t strong enough.

For women in countries with restrictive reproductive laws, the concern runs deeper: could cycle data one day be used against them if they seek healthcare?

Security audits show these fears aren’t unfounded. A 2025 assessment of 45 female health apps found that many requested excessive permissions and collected far more data than users might expect. Another study revealed that 61% of reproductive health apps contained code vulnerabilities similar to those found in other web-app security flaws, weaknesses that could put millions of users at risk.

And these aren’t just theoretical fears. In recent years, one of the most popular apps, Flo, reached a settlement with regulators after sharing sensitive data with tech giants despite promising privacy. Other trackers have been caught sending cycle information to third parties the moment users open them, and like any digital tool, they can be hacked or leak data if security is weak. That’s why fertility and period apps are often described as some of the most sensitive tools people use — and why understanding the risks is just as important as tracking the data itself.

Why It Matters

At first, it might not seem like a big deal if an app uses your logs to show you ads for pregnancy tests or vitamins. But the impact can go far beyond that.

Sensitive data can shape not only the ads you see, but the prices you’re offered or the assumptions companies make about your health and lifestyle.
In countries with restrictive laws, something as simple as a logged missed period could be misinterpreted — and even used as evidence.
Even without legal risks, many people are uncomfortable with the idea of their private health journey being packaged, analyzed, and sold.
Your cycle data tells a deeply personal story. It should stay yours, not end up in the hands of advertisers, insurers, or strangers.
You don’t need to stop using these tools. With a few simple habits, you can get the benefits they offer while keeping a tighter hold on your private data.

How to Use Fertility Apps More Safely

A few simple habits can make a big difference:

Check the privacy policy. Look for apps that clearly explain what they collect and whether they share it. If it’s vague or hard to read, that’s usually a warning sign.

Switch off permissions you don’t need. Many trackers ask for location or contact access, even though cycle tracking works fine without it.

Keep accounts separate. Don’t connect your health logs to Facebook, Google, or other social media profiles.

Share less, not more. You don’t have to fill in every optional detail. Stick to the information you really need to get value from the app.

Explore privacy-first options. Some apps are designed to store data only on your phone, without uploading it to the cloud. These can be a safer choice if you want more control.

Used this way, fertility and period trackers can still help you understand your body and plan ahead, without giving away more than you’re comfortable with.

Protect Your Most Personal Data

Cycle trackers show just how personal our digital lives have become. The same phone that stores your period logs also holds your emails, bank details, work files, and family photos. Once that information slips out, it’s hard to get back and scammers, hackers, or even shady advertisers are quick to exploit it.

That’s why it helps to keep watch over your data. Bitdefender Digital Identity Protection monitors your personal information and alerts you if it shows up in breaches or on the dark web. Instead of being blindsided, you get an early warning and the chance to act before your information is misused.

You can get it on its own or as part of a bigger security package. If you share your home with a partner, children, and parents, a family plan is usually the smarter choice. It covers everyone’s devices and data, keeping scams, hackers, and identity thieves at bay. Kids and teens are easy targets online, and older family members are often caught by phishing or fraud. A family plan gives peace of mind that no one in the household is left unprotected.

If you don’t need that yet, start with an individual plan that covers your own data and devices. You can always upgrade later as your household grows, but having protection in place today means your digital identity is safe right now.

With the right protection, you don’t have to choose between useful tools and your privacy. You can have both.

Find out more about your family safety plan, here.