AI-Powered Cycle Intelligence
Decode your cycle
Period tracking that learns with you. Predictions that sharpen over time. Insights that actually understand your body.
What is Crimson?
Crimson is a free, AI-powered period and fertility tracking app for iOS and Android that works offline-first and encrypts all health data end-to-end. It tracks 70+ symptoms, moods, and health signals across four modes: cycle tracking, trying to conceive, pregnancy, and perimenopause. Crimson uses weighted moving average algorithms that improve predictions with every logged cycle, and includes an AI assistant that provides personalized insights based on your current cycle phase, symptom history, and tracking goals.
Features
Built around how your body actually works
Six intelligently designed tools that turn raw data into cycle literacy. No guesswork. No pink-washed nonsense.
Smart Tracking
Log periods, symptoms, moods, and daily health. Auto-calculated cycle lengths with color-coded calendar phases.
AI Insights
Chat with an assistant that knows your cycle. Context-aware responses tailored to your current phase and history.
Predictions
Weighted moving averages that sharpen with every cycle. Fertile windows, ovulation, and phase detection that improves over time.
Cycle Phases
Menstrual, follicular, ovulation, luteal — know exactly where you are and what to expect next.
Pattern Recognition
Regularity scoring, historical trends, and symptom correlations visualized in elegant, actionable charts.
Quick Logging
Minimal taps to log your day. Built for the moments when you just need to record and move on.
How It Works
Start tracking in under a minute
No account required. No setup fees. Just open the app and start understanding your cycle.
Set your baseline
Enter your average cycle length and last period start date during onboarding. Crimson uses this to generate your first predictions immediately.
Log daily
Tap the "+" button to record period days, symptoms, moods, and health signals. Quick logging takes under 10 seconds. The more you log, the smarter predictions become.
Get AI insights
Crimson detects your current cycle phase and correlates symptoms across cycles. Ask the AI assistant any question — it knows your phase, history, and patterns.
Your body.
Your data.
Period.
Crimson works fully offline. Your cycle data stays on your device. Cloud sync is optional and encrypted end-to-end. We never sell, share, or monetize your health data.
Start understanding your cycle
Free to use. Private by default. Intelligence that grows with you.