Predict the start date of your next menstrual cycle.
Your Cycle Details
Select the first day of your last period and your average cycle length.
May 2026
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Next Estimated Period
June 22nd, 2026
This is an estimate. Menstrual cycles can vary due to factors like stress, diet, and health changes. This tool should not be used for medical purposes.
Period Calculator
Everything you need to know
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Comprehensive Guide to Menstrual Cycle Tracking
Menstruation is the monthly shedding of the uterine lining, occurring cyclically in menstruating individuals. Tracking your menstrual cycle helps you:
Predict your next period
Identify irregular patterns requiring medical attention
Plan activities and understand symptoms
Monitor reproductive health
Identify fertility windows
Understanding your cycle length and patterns is the foundation of reproductive health awareness.
How to Use the Period Calculator
Our period calculator predicts your next menstruation:
Enter Your Last Period Date
First day of your last menstruation
Not the last day, but the first day of bleeding
Enter Your Cycle Length
Number of days from first day of one period to first day of next
Typical range: 21-35 days
Average: 28 days
View Your Predictions
Next expected period date
Following months' predicted dates
Cycle length validation
Irregular pattern alerts if applicable
Menstrual Cycle Calculation
Basic Formula
Next Period Date = Last Period Date + Cycle Length (in days)
Example: If last period started May 1 and your cycle is 28 days
Next period = May 1 + 28 days = May 29
Calculating Average Cycle Length
If your cycles vary, track them for 3-6 months:
Average Cycle Length = Total days ÷ Number of cycles
Example: Last 3 cycles were 26, 28, and 30 days
Average = (26 + 28 + 30) ÷ 3 = 84 ÷ 3 = 28 days
What is a "Normal" Menstrual Cycle?
Standard Cycle Parameters
Parameter
Normal Range
Notes
Cycle length
21-35 days
Counted first day of period to first day of next
Menstruation duration
3-7 days
Bleeding duration
Flow volume
30-40 mL total
About 2-3 tablespoons
Bleeding patterns
Consistent month-to-month
Regular, not chaotic
Cycle Variations
What's normal:
5-7 day variation month-to-month
Occasional skipped or late periods (stress, travel, illness)
Flow variation with age
Changes in cycle length over time
What's potentially concerning:
Cycles <21 or >35 days consistently
Bleeding lasting >7 days regularly
Extremely heavy bleeding (soaking pads/tampons frequently)
Spotting between periods
Complete absence for >3 months (if menstruating)
Severe cramping
Phases of the Menstrual Cycle
Menstruation (Days 1-5)
Duration: 3-7 days (5 days average)
What happens:
Uterine lining sheds through cervix
Discharge includes blood, tissue, and fluid
Hormone levels drop
Typical flow:
Days 1-2: Heaviest flow
Days 3-4: Moderate flow
Days 5+: Light flow or spotting
Common experiences:
Abdominal and lower back cramping
Mild to severe fatigue
Mood changes
Bloating
Headaches (for some)
Breast tenderness
Follicular Phase (Days 6-13)
Duration: 8-14 days (overlaps with menstruation start)
If no fertilization, hormone levels decline toward end of phase
Common experiences:
PMS symptoms (irritability, mood swings, fatigue)
Bloating and water retention
Food cravings
Breast tenderness (progesterone effect)
Acne (for some)
Sleep changes
Reduced energy
Understanding Period Symptoms (PMS and PMDD)
Premenstrual Syndrome (PMS)
When it occurs: 5-11 days before period
Common symptoms:
Mood changes (irritability, sadness, anxiety)
Fatigue and low energy
Bloating and water retention
Breast tenderness
Food cravings (especially sweets/carbs)
Headaches
Sleep disturbances
Acne breakouts
Relief strategies:
Exercise (improves mood, reduces cramps)
Calcium and magnesium supplements
Heat therapy for cramping
Reducing caffeine and salt
Sleep optimization
Stress management
Premenstrual Dysphoric Disorder (PMDD)
When it occurs: 5-11 days before period
Distinction from PMS:
More severe mood symptoms
Interferes significantly with daily functioning
Present in ~3-8% of menstruating people
Requires medical evaluation and often treatment
Symptoms include:
Severe depression or hopelessness
Severe anxiety or tension
Extreme mood swings
Significant irritability or anger
Difficulty concentrating
Fatigue
Food cravings or binge eating
Medical management: Antidepressants, hormonal contraceptives, or other medications may help
Tracking Your Cycle Effectively
What to Record
Data Point
How Often
Why It Matters
First day of period
Monthly
Foundation for calculations
Period duration
Monthly
Identifies length changes
Flow heaviness
Cycle
Tracks changes
Symptoms (cramps, mood)
Daily
Identifies patterns
Cervical mucus
Daily (if tracking fertility)
Most reliable fertility sign
Basal temperature
Daily (if tracking fertility)
Confirms ovulation
Activity and exercise
Daily
See correlations with cycle
Using a Period Tracking App
Benefits of apps:
Automatic prediction of next period
Pattern identification over months
Symptom tracking
Medication reminders
Backup tracking (not reliant on memory)
Sharing data with healthcare providers
Recognizing Irregular Patterns
Pattern
Possible Cause
When to See Doctor
Sudden cycle length change
Stress, illness, hormones
After 2-3 irregular cycles
Missed periods
Pregnancy, stress, underweight, overweight
Immediately if not pregnant
Very heavy periods
Fibroids, polyps, hormonal imbalance
If affecting quality of life
Spotting between periods
Hormonal contraceptives (normal initially)
If persistent or new
Severe cramping
Endometriosis, fibroids
If interfering with daily life
Cycle Syncing (Using Cycle Knowledge)
Some people adjust activity and nutrition based on cycle phases:
Follicular Phase (High Energy)
Best for: High-intensity training, competition
Nutrition: Can handle higher carbs/calories
Activity: Peak performance window
Ovulation (Peak Performance)
Best for: Maximum effort workouts
Mood: Often more social
Strength: May peak around ovulation
Luteal Phase (Lower Energy)
Best for: Moderate activity, strength training
Nutrition: Higher protein can help satiety
Rest: Prioritize recovery and sleep
Note: Individual variation is significant; "cycle syncing" works for some but not all.
When to See a Healthcare Provider
Irregular or Concerning Patterns
Schedule an appointment if you experience:
Cycle length consistently <21 or >35 days
Bleeding lasting >7 days
Soaking through pads/tampons more than hourly
No period for 3+ months (if previously regular)
Severe cramping interfering with daily life
Abnormal bleeding between periods
Sudden major changes in cycle
Significant PMS/PMDD symptoms
Questions to Discuss
Is my cycle normal?
Should I track my cycle differently?
Are my symptoms typical?
How can I manage PMS?
Could something be wrong?
Frequently Asked Questions
How long should my period last?
Normal: 3-7 days, with 5 days being average. Anything 3-7 days is considered normal. Longer or shorter may warrant discussion with your doctor.
Why is my cycle irregular?
Common causes include:
Stress
Illness
Changes in exercise
Weight changes
Travel or jet lag
Hormonal contraceptive changes
Breastfeeding
Age (teens and perimenopausal)
Polycystic ovary syndrome (PCOS)
Thyroid disorders
Can I predict my period if my cycle is irregular?
With difficulty. Use average cycle length if cycles vary <5 days. If more irregular, track for 6 months to find patterns. Apps help identify patterns human memory doesn't.
Is it normal to skip a period?
Occasionally, yes (stress, illness, travel). Regularly skipping is not normal and warrants evaluation. Completely missing periods requires investigation.
Can I get pregnant during my period?
Rarely, but yes. Sperm can survive several days, and if ovulation occurs earlier than expected, pregnancy is possible.
Should I use period products differently based on my cycle?
Some people change from pads to tampons to cups based on flow. Most use what's comfortable for each day's flow volume. Experiment to find what works.
Does exercise affect my menstrual cycle?
Excessive exercise (especially in underweight people) can suppress periods. Normal exercise doesn't disrupt regular cycles.