☾ Period Calendar & Predictor
Predict your upcoming period dates for the next 3 months to plan your workouts.
Sync to Your Cycle
Get personalized daily workouts, cycle tracking, and custom nutrition plans matching your current phase inside the Moona Web App.
Start Free AI Coaching ✦🧬 Tracking and Predicting Your Menstrual Cycles
Predicting your upcoming period dates is crucial for cycle syncing your fitness, planning your work-rest schedule, and managing hormonal symptoms proactively.
✦ How accurate are period predictors? ↓
Most mathematical models are highly accurate if your cycle is regular. They use your historic average cycle length to project start dates. However, hormonal disruptions, severe stress, diet changes, or illnesses can delay ovulation and make predictions less accurate.
✦ What is considered a regular cycle length? ↓
A regular menstrual cycle typically lasts between 21 and 35 days (up to 45 days in young adults). The key indicator of regularity is consistency: if your cycle length varies by less than 5 to 7 days from month to month, it is clinically considered regular.
✦ How can I log irregular periods in a predictor? ↓
For irregular cycles, standard static predictors can only offer a rough estimate. We recommend averaging your last 3-6 cycles for the math, and using the Moona App for daily tracking of physical bio-markers like basal temperature and cervical mucus.
✦ Does stress really shift my predicted period date? ↓
Yes. Psychological and physical stress elevates cortisol, which can suppress gonadotropin-releasing hormone (GnRH) and delay ovulation. Since your period arrives ~14 days after ovulation regardless of cycle length, a delayed ovulation pushes back the entire prediction. Acute stress can shift a single cycle by 1–2 weeks.
✦ Can I use this predictor while breastfeeding? ↓
Breastfeeding suppresses ovulation through elevated prolactin levels. Cycles typically return 6–18 months postpartum, and the first several cycles are often irregular. The predictor becomes reliable only after you've had at least 3 consecutive regular cycles post-breastfeeding.
✦ How does age affect cycle regularity? ↓
Cycles are often irregular during the first 2–3 years after menarche and again in the 5–10 years before menopause (perimenopause). During peak reproductive years (roughly 20–40), most women have predictable cycles. After age 40, cycles may shorten from 28 to 24–25 days as ovarian reserve declines.
📖 Getting Started with Period Predictions
Enter the start date of your most recent period and your average cycle length. The predictor calculates your next three period start dates by adding cycle-length intervals from that anchor date.
For best accuracy, base your cycle length on the last 3–6 months of data. If your cycles vary by more than 7 days, use the shortest recent cycle as a conservative estimate.
📊 Reading Your Predicted Dates
Each predicted date represents the most likely first day of bleeding based on your stated average. Dates further into the future carry more uncertainty because factors like stress, illness, and travel can shift ovulation timing.
The calendar also highlights approximate fertile windows (days 10–16 of each cycle by default). These are rough estimates — for precise ovulation tracking, use the dedicated Ovulation Calculator tool.
⚕️ Medical Considerations
See a healthcare provider if you miss three or more consecutive periods (amenorrhea), if your cycle suddenly becomes irregular after being predictable, or if you experience heavy bleeding that soaks through a pad or tampon every hour. These symptoms may indicate hormonal imbalances, uterine fibroids, or thyroid issues that require clinical evaluation.