AI-Powered Cycle Intelligence
The AI period tracker that decodes your cycle
Free AI tracking for all four stages — cycle, trying to conceive, pregnancy, and perimenopause. Predictions that get sharper the more you log. Pro unlocks unlimited AI, patterns, and reports.
What is Crimson?
Crimson is a free AI-powered period and fertility tracking app for iOS and Android with secure cloud sync and privacy-first design. It tracks 70+ symptoms, moods, and health signals across four modes: cycle tracking, trying to conceive, pregnancy, and perimenopause tracking. 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.
Four Modes
One app for the whole road
Your body doesn't stay in one chapter, and neither should your tracker. Switch modes whenever life changes — your history comes with you.
Know what's coming, and why
Periods, 70+ symptoms, moods, and the four cycle phases. Predictions sharpen with every cycle you log, so the guesswork fades instead of repeating.
Read the cycle tracking guide →Find your fertile window
Ovulation prediction, fertile-window forecasting, basal body temperature, and cervical mucus logging — the signals that actually narrow the window.
See the ovulation tracker →Week by week, no scrambling
Gestational week and trimester, baby size, kick counter, contraction timer, appointments, and weight — tracked in the same app you already trust.
Explore pregnancy mode →Proof your symptoms are real
Hot flash logging with severity and triggers, hormone test results, and irregular-cycle patterns — the record that makes a doctor's appointment count.
Explore perimenopause mode →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. See how Crimson compares to Flo and Clue.
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. Need a quick estimate? Try our free ovulation calculator.
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
Quick, free sign-up. A one-minute onboarding. Then start understanding your cycle. Want the deeper dive first? Read the full cycle tracking guide.
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.
Your cycle data is securely synced to the cloud and protected. We never sell, share, or monetize your health data.
Start understanding your cycle
Free to use. Private by default. Pro unlocks more.