Flo vs Clue vs Natural Cycles (2026): an honest comparison

Flo, Clue and Natural Cycles side by side: what they cost, where your data goes, what they can and cannot do. With sources, as of October 2026.

Written by the PERIOD. team. We make a cycle app ourselves, so read this as a comparison by makers, with sources so you can check everything yourself. As of October 2026.

Short answer: Natural Cycles is the only one of the three cleared as contraception (FDA), but you always pay and you need a thermometer or wearable. Clue is European and has a free version. Flo is the biggest, with the most features, and has a privacy history you should know about. If you mainly want to understand your cycle without your health data becoming a business model, also look at a European app that does not sell your data.

At a glance

• Natural Cycles: FDA-cleared as contraception. According to the company 93% effective with typical use and 98% with perfect use. Subscription and a measuring device required (naturalcycles.com, MobiHealthNews on the FDA clearance).
• Clue: based in Berlin, covered by the GDPR. Free version plus paid Clue Plus, price varies by country. Clue says it never sells your health data (helloclue.com, Clue Plus pricing).
• Flo: the largest cycle app in the world, free version plus Flo Premium. In 2021 Flo settled with the US Federal Trade Commission over sharing health data with analytics services including Facebook's and Google's. Flo denied wrongdoing (FTC).

1. Privacy: where does your data go?

This is the biggest difference. According to the FTC, Flo shared events such as "pregnant" with marketing and analytics companies until 2019. A US class action led to settlements totalling 59.5 million dollars (Google 48 million, Flo 8 million, Flurry 3.5 million), and in August 2025 a jury found Meta liable (HIPAA Journal, Fierce Healthcare). All parties denied wrongdoing. Flo has since added an anonymous mode.

Clue is based in Germany and therefore under the strictest privacy law there is. Natural Cycles is a Swedish medical company and works under medical device rules.

Check it yourself: search the privacy policy for "sell", "partners", "advertising" and "transfer". No list of sub-processors means no transparency.

2. What does it cost?

• Natural Cycles: no free version, you need a monthly or yearly subscription plus a thermometer or compatible wearable.
• Clue and Flo: free basics, extra features in a subscription. Prices vary by country, you see them in the app.

3. What is each app good at?

• You want hormone-free contraception: Natural Cycles is the only one of these three with official clearance for that. A regular cycle app is not contraception.
• You want to understand your cycle and track symptoms: Clue and Flo both do this, Flo with more content and community, Clue calmer and more science-led.
• You want your data to stay in Europe and never be sold: Clue, or an app like PERIOD.

Where does PERIOD. fit?

PERIOD. is a Dutch app. Your data is stored encrypted in Frankfurt, we sell nothing, and your health data never goes to advertisers. To measure which of our own ads work we share a few events without health data, such as "trial started"; that is plainly stated in our privacy policy. The basics are free. PERIOD. plus costs 3.99 per month or 34.99 per year. PERIOD. is not contraception.

FAQ

Which app is most reliable for contraception? Of these three, only Natural Cycles is cleared as contraception. Always talk to your doctor or midwife.

Is a European app automatically safer? Not automatically, but the GDPR gives you more rights and the app more duties.

General information, not medical advice. Brand names belong to their owners. Prices and features change; always check the current details in the app itself.

Prefer an app that does not sell your data? Download PERIOD. on the App Store or on Google Play. The basics stay free.