Cycle Tracker
Ovulation, Period & Fertile Window Prediction
How It Works
The Algorithm
We predict ovulation by subtracting your luteal phase (default 14 days) from your cycle length. Your fertile window spans 5 days before ovulation through ovulation day. The next period is simply your LMP plus cycle length. If you enter a BBT rise date, we use that as confirmed ovulation instead of the estimate — this overrides the algorithm with real data.
How to Use
Enter your last period start date and average cycle length. Add optional BBT rise date for precision. The chart visualizes your current position in the cycle: period days (dark pink), fertile window (gold), ovulation (marker), and today (dot). Save predictions to track cycle regularity over time.
Pro Tips
- Track for 3+ months to establish your true average — one month is not enough for accurate prediction.
- If your luteal phase is consistently shorter than 12 days, mention it to your provider — it can affect fertility.
- The BBT field is optional but powerful: it turns an estimate into a confirmed, personalized prediction.
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