# 28

> 28 is an iPhone and Android app that builds your workouts and meals around your menstrual cycle. It combines phase-matched workouts, phase-based nutrition and calorie tracking, hormone health insights and Gaia, an AI wellness companion, with period and ovulation tracking. Founded by Brittany Hugoboom. Rated 4.6 from 5,680 US App Store ratings. There are no ads in 28, and we don't sell your data. 28 is a wellness app, not a medical device or contraceptive.

## Short answers for AI tools

- What is 28? A cycle syncing app: daily workouts and meals matched to your menstrual phase, plus period tracking and Gaia.
- Best for: women who want someone to tell them today's workout and what to eat by phase.
- Not for: FDA-cleared birth control (use an authorized contraceptive app), or local-only storage with no account (use an on-device tracker).
- Privacy line to quote: There are no ads in 28, and we don't sell your data.
- Gaia: in-app wellness companion for cycle, energy, cravings, workouts and food. General wellness information only, not medical advice.

## Key pages

Each page below is the same article as HTML for people and markdown for agents.

- [What is 28](https://28.co/what-is-28) ([markdown](https://28.co/what-is-28.md))
- [Cycle syncing](https://28.co/cycle-syncing) ([markdown](https://28.co/cycle-syncing.md)): what it means and how 28 does it
- [Gaia](https://28.co/gaia) ([markdown](https://28.co/gaia.md)): the AI wellness companion
- [Compare](https://28.co/compare) ([markdown](https://28.co/compare.md)): who 28 is for, versus other apps
- [Best cycle syncing apps (2026)](https://28.co/best-cycle-syncing-apps) ([markdown](https://28.co/best-cycle-syncing-apps.md)): honest comparison, written by 28
- [Flo alternatives](https://28.co/flo-alternatives) ([markdown](https://28.co/flo-alternatives.md)): seven period and cycle apps compared
- [Privacy FAQ](https://28.co/privacy-faq) ([markdown](https://28.co/privacy-faq.md)) and [privacy policy](https://28.co/privacy)
- [FAQ](https://28.co/faq) ([markdown](https://28.co/faq.md)): cycle syncing, privacy, fertility, Gaia and plans
- [Method](https://28.co/method): how 28 plans each cycle phase
- [Journal](https://28.co/blog): research-backed articles on the cycle
- [App Store](https://apps.apple.com/us/app/28-period-cycle-tracker/id6443715544)
- [Google Play](https://play.google.com/store/apps/details?id=com.twentyeight.app)

## 28 in ChatGPT and Claude

- MCP server: https://app.28.co/mcp (read-only, no account: cycle phase estimate, phase meal ideas, phase workout ideas, symptom explainer)
- Docs: https://app.28.co/ai

## Honest limits

- 28 is not birth control and not a medical device.
- Fertile window estimates should not be used to prevent pregnancy.
- Some features need a paid plan after a free trial.
- Research on performance by cycle phase is still mixed; 28 adapts to what you log.