Period Calculator - Free Online Menstrual Cycle Tracker & Calendar
Period Calculator
Typical range: 21-35 days (average 28)
Typical range: 3-7 days (average 5)
Track Your Cycle
Understanding your menstrual cycle helps you predict periods, fertile days, and PMS symptoms. A regular cycle is typically 24-32 days.
Enter your cycle information and click "Calculate Next Period" to see your personalized menstrual calendar and predictions
What is a Period Calculator?
A period calculator is a health tool designed to help women track their menstrual cycles and predict future period dates. By entering the first day of your last period and your average cycle length, the calculator estimates when your next period will start, when you're most fertile, and when PMS symptoms might begin.
The menstrual cycle is the monthly hormonal cycle that prepares the body for pregnancy. It begins on the first day of menstruation (day 1) and ends the day before the next period starts. The average cycle length is 28 days, but normal cycles can range from 21 to 35 days. Understanding your cycle helps you anticipate physical and emotional changes throughout the month.
Our period calculator provides a comprehensive 6-month calendar showing your predicted period dates, fertile windows, ovulation days, and PMS symptom timelines. It also analyzes your cycle regularity, helping you identify patterns or potential irregularities that may warrant medical attention.
Regular period tracking is essential for reproductive health awareness, family planning, and identifying potential health issues early. Whether you're trying to conceive, avoid pregnancy, or simply understand your body better, a period calculator is an invaluable tool for menstrual health management.
How to Use the Period Calculator
Enter Last Period Date
Input the first day of your most recent menstrual period. This marks day 1 of your cycle.
Enter Cycle Length
Specify your average cycle length (21-45 days). If unsure, use 28 days as a starting point.
Enter Period Duration
Input how many days your period typically lasts (2-10 days, average 5 days).
View Your Calendar
Get your next period date, fertile window, ovulation day, PMS timeline, and 6-month calendar.
Understanding Your Menstrual Cycle
The menstrual cycle consists of four distinct phases, each governed by hormonal changes:
🩸 Menstrual Phase (Days 1-5)
The period itself. The uterine lining (endometrium) sheds, resulting in menstrual bleeding. Hormone levels are at their lowest.
🌱 Follicular Phase (Days 1-13)
Overlaps with menstruation. FSH stimulates follicle growth in ovaries. Estrogen rises, thickening the uterine lining for potential pregnancy.
✨ Ovulation Phase (Day 14)
A surge in LH triggers the release of a mature egg from the ovary. This is the most fertile time of your cycle, lasting about 24 hours.
🌙 Luteal Phase (Days 15-28)
The corpus luteum produces progesterone, further thickening the uterine lining. If pregnancy doesn't occur, hormone levels drop, triggering menstruation.
Understanding PMS and Menstrual Symptoms
Premenstrual Syndrome (PMS) refers to a collection of physical and emotional symptoms that occur during the luteal phase, typically 5-11 days before your period. Up to 75% of menstruating women experience some form of PMS.
Common PMS Symptoms:
Physical Symptoms:
- Bloating and water retention
- Breast tenderness and swelling
- Fatigue and low energy
- Headaches or migraines
- Food cravings (especially sweets)
- Acne breakouts
- Muscle or joint pain
Emotional Symptoms:
- Mood swings
- Irritability or anger
- Anxiety or tension
- Depression or sadness
- Difficulty concentrating
- Changes in sleep patterns
- Social withdrawal
Managing PMS: Lifestyle modifications can significantly reduce PMS symptoms. Regular exercise, balanced nutrition (limiting salt, sugar, and caffeine), stress management techniques, adequate sleep, and staying hydrated all help. For severe symptoms that interfere with daily life, consult a healthcare provider about treatment options including hormonal birth control or other medications.
External Resources & Further Reading
For more comprehensive information on menstrual health, cycle tracking, and reproductive wellness, explore these authoritative medical resources:
ACOG - Menstrual Health
Official guidance on menstrual cycles, irregular periods, and reproductive health from the American College of Obstetricians and Gynecologists.
acog.org →Mayo Clinic - Menstrual Cycle
Evidence-based information on understanding your menstrual cycle, tracking periods, and identifying abnormalities.
mayoclinic.org →OWH - Menstrual Cycle Guide
Comprehensive menstrual health information from the Office on Women's Health, U.S. Department of Health and Human Services.
womenshealth.gov →NIH - Menstruation Research
Scientific research and clinical information on menstruation, PMS, and menstrual disorders from the National Institutes of Health.
nih.gov →Related Calculators
Frequently Asked Questions
How does a period calculator work?
A period calculator predicts your next period date by adding your average cycle length to the first day of your last period. It also calculates your fertile window (approximately 5-6 days around ovulation) and potential PMS symptom start date (typically 5-11 days before your period).
What is a normal menstrual cycle length?
A normal menstrual cycle typically ranges from 21 to 35 days, with the average being 28 days. Cycles between 24-32 days are considered regular. Variations of up to 7-9 days from month to month are common, especially in the first few years after menstruation begins and in the years approaching menopause.
How accurate are period calculators?
Period calculators are most accurate for women with regular cycles. They provide estimates based on your average cycle length but cannot account for factors like stress, illness, travel, or hormonal changes that may affect timing. For best accuracy, track your cycles for at least 3-6 months and update your average cycle length regularly.
What should I do if my period is irregular?
If your menstrual cycle varies by more than 7-9 days each month, it is considered irregular. Track your cycles for at least 3 months to identify patterns. Common causes include stress, weight changes, excessive exercise, hormonal imbalances, or underlying medical conditions. Consult a healthcare provider if irregularity persists, especially if accompanied by heavy bleeding, severe pain, or missed periods.
What are PMS symptoms and when do they start?
PMS (Premenstrual Syndrome) refers to physical and emotional symptoms that occur 5-11 days before menstruation. Common symptoms include bloating, breast tenderness, mood swings, irritability, fatigue, food cravings, and headaches. Symptoms typically resolve within a few days after menstruation begins. Severe PMS symptoms may indicate PMDD (Premenstrual Dysphoric Disorder) and should be evaluated by a healthcare provider.
When should I see a doctor about my menstrual cycle?
Consult a healthcare provider if you experience: periods lasting longer than 7 days, cycles shorter than 21 days or longer than 35 days, severe pain that interferes with daily activities, heavy bleeding requiring pad/tampon changes every 1-2 hours, bleeding between periods, missed periods (not due to pregnancy), or severe PMS symptoms affecting your quality of life.