Period Calculator
Predict your next period and track menstrual cycle patterns. A normal cycle is 21-35 days with bleeding lasting 2-7 days. Regular tracking helps identify irregularities, fertile windows, and potential health concerns.
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Key values and context for this tool: • Normal Cycle: 21-35 Days • Average: 28 Days • Period Length: 2-7 Days
Ready to run the numbers?
Why: This page explains what the Period calculator does, what to enter, and how to read the results—without repeating the overview above.
How: Enter your values in the calculator fields below, keep units consistent, then run the calculation to see results and any step-by-step work shown on this page.
Run the calculator when you are ready.
Sample Scenarios
🔄 Regular 28-Day
Textbook cycle, 5-day period
⚡ Short (24 days)
Shorter cycle, earlier ovulation
📅 Long (35 days)
Longer cycle, later ovulation
📊 Irregular
Variable cycle, careful tracking
⚠️ Severe PMS
Regular cycle, significant PMS
👶 Trying to Conceive
28-day cycle, 6-month forecast
Enter Your Cycle Information
For informational purposes only — not medical advice. Consult a healthcare professional before acting on results.
What is a Period Calculator?
A period calculator predicts your menstrual cycle, including next period, ovulation, fertile window, and PMS symptoms. A normal cycle is 21-35 days with bleeding lasting 2-7 days.
Period Predictions
Multi-month predictions, period start/end dates
Fertility Window
Ovulation date, 6-day fertile window
PMS Awareness
PMS window prediction, preparation reminders
How Does the Period Calculator Work?
The menstrual cycle has four phases: menstruation, follicular, ovulation, and luteal. Knowing your average cycle length and last period date allows prediction of future cycles.
When to Use the Period Calculator
📆 Life Planning
Plan vacations, events, weddings around your cycle
👶 Family Planning
Conception timing or natural family planning
🩺 Health Monitoring
Track patterns, identify irregularities
Period Calculation Formulas
Next Period
Next Period Start = Last Period Start + Cycle Length
Ovulation Day
Ovulation Day = Cycle Length - 14 (luteal phase)
Fertile Window
Fertile Window = Ovulation Day - 5 through Ovulation Day
Normal Cycle Ranges
Normal cycle: 21-35 days. Average: 28 days. Period length: 2-7 days. Variations of a few days are normal.
Cycle Phases Explained
- Menstrual: Bleeding, days 1-5 typically
- Follicular: Follicles develop, preparing for ovulation
- Ovulatory: Egg released, fertile window
- Luteal: Post-ovulation, PMS may occur in late luteal
Irregular Cycles
Irregularity can be caused by stress, weight changes, PCOS, thyroid disorders, perimenopause. Use an average of 3-6 cycles. Consider OPKs or BBT for more accuracy.
Fertility Awareness
The period calculator shows predicted fertile days but should not be used as sole contraception. Combine with BBT and cervical mucus for fertility awareness methods.
Disclaimer
This tool is for educational purposes. Predictions depend on cycle regularity. Consult a healthcare provider for medical advice.
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