How to choose a private period tracker: a checklist

By the Twilune team, checked against the sources below · October 27, 2026 · 7 min read

A private period tracker keeps your cycle data on your own device, does not force you to make an account, shows no ads, and tells you plainly what it does with your information. Use the seven-point checklist below before you download anything. Then check any app against it, including ours.

Why does period tracker privacy matter?

A period tracker holds some of the most personal data you have: when you bleed, how you feel, what symptoms you notice, sometimes your sex life or pregnancy plans. What protects it depends heavily on what the app's maker chooses to do and what it promises in its policy, so those are the things to check.

That gap has been tested. In January 2021 the US Federal Trade Commission (FTC) announced a settlement with Flo Health, the maker of the Flo Period & Ovulation Tracker. The FTC alleged that Flo shared sensitive health data from millions of users with marketing and analytics firms, including Facebook and Google, despite promising to keep that data private. The FTC finalized the order in June 2021.

Under the order, Flo must get users' affirmative consent before sharing their personal health information, get an independent review of its privacy practices, notify affected users, and tell third parties that received the data to destroy it. The FTC's pages describe these as allegations and a settlement. They do not state whether Flo admitted wrongdoing. We mention this case because it is the clearest documented example of why the checklist below exists, not to suggest every app behaves this way.

Concern grew again after the US Supreme Court's 2022 decision in Dobbs v. Jackson Women's Health Organization. A 2025 study in the Journal of Medical Internet Research notes that after a draft of the ruling leaked in May 2022, many users questioned which apps were safe, and some switched to apps with stronger privacy practices. The same authors warn that data such as location, IP addresses and period tracking could expose people to legal risk where abortion is restricted.

The picture is not simple. A separate survey study in the journal Contraception looked at women aged 18 to 44 in five US states. It found that use of period- or fertility-tracking technology actually rose after Dobbs in four of the five states. So many people kept using these apps. That makes it more useful to choose carefully, not less.

What should be on a private period tracker checklist?

Here are the seven things worth checking. None of them needs technical knowledge. Most can be answered from an app's store page and privacy policy in a few minutes.

1. Where is your data stored: on your phone or in the cloud?

This is the big one. If your data lives only on your device, a company has no server copy to lose, sell or hand over. If it lives in a cloud account, you are trusting that company, its staff and its security.

Cloud storage is not automatically bad. It lets you move to a new phone easily. But ask the question, and prefer apps that say clearly where the data lives.

2. Do you need an account?

An account usually means an email address or phone number linked to your cycle history. An app that works without one has no profile to link to you. If an account is required, find out why, and what happens to it if you leave.

3. Does it show ads or use third-party tracking tools?

Many apps include software development kits (SDKs) from other companies, such as ad networks and analytics tools. Each one can send information about your use of the app to someone else. The Flo case was about this kind of sharing.

Look for a plain statement of "no ads" and "no ad SDKs". If the app does use analytics, the policy should say exactly what is sent, and the setting should be optional.

4. What does the privacy policy say about sharing and law enforcement?

Read three parts of the policy:

• Sharing. Does it say who gets your data and why? Vague phrases like "trusted partners" are a warning sign.
• Legal requests. Does it say what happens if a government or court asks for your data? A 2025 review of four popular reproductive health apps found that policies were often unclear on this, and that some gave little detail on how sharing works.
• Selling. Does it say clearly that it does not sell your data?

The same review found that three of the four apps it examined shared some data with third parties for marketing. It is a small sample, and policies change, so check the current version yourself.

5. Can you export and delete your data?

You should be able to take your history with you and remove it completely. Look for a backup or export option, and for a delete function that clearly says it removes everything, not just logs you out. If deletion means emailing support, that is a weaker answer.

6. Is there an app lock?

Privacy is not only about companies. A partner, a family member or a stranger holding your unlocked phone can open the app. A PIN or biometric lock inside the app adds a second layer on top of your phone's screen lock.

7. Is the company honest about what it is?

A good sign is an app that says what it is not. For example, that it is not a medical device, or that predictions are estimates. Be wary of apps that make big promises about health outcomes while saying little about data.

How does Twilune answer each item?

We would rather show our answers than ask you to trust a slogan. Twilune is a period tracker and mood app for Android that is in closed testing on Google Play. Here is how it fits the checklist.

A few honest details matter here:

• The Google backup is yours. If you turn on your phone's backup, your data is protected by your Google account and your device settings. That is outside Twilune's control. If you do not want any copy off your phone, turn that backup off.
• Optional partner link. Twilune has an optional live partner link. Its content is end-to-end encrypted and carries only what you choose to share. The server can still see when it updates, and when your phase changes if your partner turns on notifications.
• The companion answers on your device. Siderelle answers on your phone. An online mode is optional and asks first; it sends your recent Siderelle messages and a small cycle context to our AI provider, never your logs.
• What is free. Tracking, predictions, the calendar, the forecast, the SOS screen and the core calm tools are free forever.

Nothing here means Twilune is the right app for everyone. If you want to sync across several devices, for example, a cloud-based app may suit you better. What matters is that you choose knowingly.

What else can you do to protect your cycle data?

• Check your phone, not just the app. Use a screen lock, and turn off previews of notifications if the wording would give anything away.
• Be careful with permissions. A period tracker rarely needs your location, contacts or microphone.
• Re-read the policy now and then. Companies change them, and a change in ownership can change what happens to your data.
• Log only what you want to log. Most apps work with just dates. Symptoms, moods and notes are optional extras.
• Think about where you live. If you are somewhere that restricts reproductive healthcare, a device-only app with an app lock is a more careful choice. This is general information, not legal advice.

What is the short version?

Ask where your data lives, whether you need an account, who else receives information, what the policy says about legal requests, whether you can export and delete, and whether there is an app lock. Then decide who you trust with the answer. If you track your cycle for health reasons, a good place to start learning is the four phases of the menstrual cycle.

Frequently asked questions

This article is general information, not medical advice. If something worries you, or your symptoms are severe or getting in the way of your life, talk to a doctor. If you are thinking about harming yourself, call your local emergency number now.