Flo is the dominant period tracker — #1 by market share, 77 million monthly active users, $275M revenue. It is excellent at what it does: helping women understand their own cycle with clinical-grade predictions and health insights. In October 2023 it launched Flo for Partners, which is the closest any competitor has come to Yuni's territory.

Flo for Partners works like this: she shares a code, you install Flo, and you get a read-only calendar view plus daily "story cards" about what she might be feeling. The framing is almost entirely fertility and TTC (trying to conceive) — it explains when she's ovulating, not how to show up for her during PMS. You cannot use it independently; the partner experience requires her to be an active Flo subscriber and invite you in.

On privacy: in 2021, the FTC settled with Flo for sharing intimate health data — menstrual dates, pregnancy status, fertility intentions — with Facebook, Google, and other ad platforms, despite explicit privacy promises to users. Flo was required to notify all affected users and have third parties destroy the data. Their "Anonymous Mode" launched afterward is a PR response, not a privacy-first design.

Stardust is a cycle tracker with a cosmic twist — moon phases, daily affirmations, and a community sharing feed. It does have a Partner Mode: she invites you with a code, and you get push notifications like "be extra considerate today." That's a start.

But the partner experience is entirely notification-driven. There's no dedicated guidance, no daily actions, no context about what this phase actually means for how you should behave. You get a ping — you don't get a playbook.

Stardust also requires a phone number or account, and a 2022 investigation by TechCrunch and Privacy International found its privacy claims weren't airtight — third-party SDKs were present that could expose data.

Clue is one of the best-regarded period trackers: science-backed, GDPR-compliant, headquartered in Berlin. If she wants to track 200+ health factors with clinical rigour, Clue is excellent. It even has Clue Connect — a paid sharing feature that gives you a read-only view of her period dates.

But a calendar of her period dates tells you nothing about how to be supportive. There's no guidance for you, no phase explanation, no "here's what she needs during PMS." You're just watching the calendar.

Clue Connect also requires a Clue Plus subscription ($40/year) for the sharing side, and of course a full account with cloud storage.

Natural Cycles is FDA-cleared as a contraceptive — it uses basal body temperature to predict fertile and non-fertile days. If you and your partner are using it for birth control or trying to conceive, it serves a specific medical purpose. It is not a cycle tracker in the general sense.

There are no partner features whatsoever. No sharing, no guidance, no way to use it as a partner. It also requires daily temperature measurement, a mandatory subscription (~$150/year), and cloud storage of very sensitive health data.

A class action lawsuit filed in 2025 alleges Natural Cycles embedded trackers from third-party advertisers — including TikTok and Google — that transmitted users' reproductive health data without consent.

Lively is the closest competitor in concept. It takes a "cycle syncing" approach — tailoring nutrition, exercise, and mood advice to each cycle phase. It has a Partner Syncing feature that lets partners see the current phase, energy level, and even a mood indicator she can update. Partners can send a "thinking of you" nudge.

But Lively's partner feature still lives inside an app fundamentally designed for the person menstruating. The partner interface has no dedicated home screen, no daily guidance specific to the partner's role, and no explanation of what each phase means in terms of relationship dynamics.

There's also no Apple Watch or Lock Screen widget for the partner — to check her phase, you open the app, navigate to partner view, and find it.

Premom is a fertility-focused app for people trying to conceive. It reads LH test strips via your phone camera, charts basal body temperature via Bluetooth thermometers, and predicts fertile windows with high accuracy. It is an excellent tool for a specific purpose — getting pregnant.

There are no partner features. Premom is not relevant for general cycle phase awareness or relationship support. It is also tightly coupled to hardware (their branded test strips and thermometer), creating vendor lock-in.

In 2023, the FTC charged Easy Healthcare (Premom's developer) with sharing sensitive reproductive health data with third-party analytics firms, including two based in China. The company paid $200,000 in civil penalties and was barred from sharing health data for advertising.