Period Calculator (Menstrual Cycle Tracker)
Track your menstrual cycle with our free Period Calculator. Enter your last period date and cycle length to get your next period date, ovulation window, and current cycle phase. Stay informed about your reproductive health with this easy-to-use tool based on standard cycle tracking methods.
Period Calculator
Your Cycle Results
How to Use the Tool
1. Enter LMP
First day of your last period.
2. Set cycle details
Cycle length & period length.
3. Get insights
Next period, ovulation & phase.
How It's Calculated
Key Formulas
- Cycle Day: (Days since LMP % Cycle Length) + 1
- Next Period: LMP + (Cycle Length × (Cycles + 1))
- Ovulation: Cycle Length − 14 (luteal phase)
Phases
- Period: Day 1 – Period Length
- Follicular: After period until ovulation
- Ovulation: ~14 days before next period
- Luteal: After ovulation until next period
About Menstrual Cycles
What is a Menstrual Cycle?
The menstrual cycle is the monthly series of changes a woman's body goes through to prepare for pregnancy. The average cycle is 28 days, but normal cycles range from 21 to 35 days. This tool helps you track your cycle, predict your next period, and identify your fertile window.
Cycle Phases:
- Menstrual Phase: Shedding of the uterine lining (days 1–5)
- Follicular Phase: Follicles develop and estrogen rises
- Ovulation: Release of a mature egg (around day 14)
- Luteal Phase: Uterine lining thickens for implantation
Limitations of This Tool
- Assumes a regular cycle length — irregular cycles may produce less accurate predictions.
- Does not account for cycle variability, stress, illness, or lifestyle factors.
- Not a substitute for medical advice or pregnancy prevention methods.
- Ovulation prediction is based on a standard 14-day luteal phase — individual variations exist.
Trust & Privacy
Your data stays in your browser. All calculations happen locally. We never send your data to any server.
No registration or login required. Your privacy is 100% protected.
Based on standard reproductive health methods. Our tool follows established cycle tracking principles.
No cookies used for tracking. Your history is stored locally in your browser's localStorage.
Real-World Examples
LMP: Jan 1, Cycle: 28 days, Period: 5 days
Next Period: Jan 29
LMP: Feb 14, Cycle: 32 days, Period: 4 days
Next Period: Mar 17
LMP: Mar 10, Cycle: 26 days, Period: 6 days
Ovulation: Mar 22
Frequently Asked Questions
References
- American College of Obstetricians and Gynecologists. Menstrual Cycle: A Guide. acog.org
- World Health Organization. Reproductive Health. who.int
- National Institutes of Health. Menstrual Cycle Basics. nichd.nih.gov