Period Calculator
Predict your next period and track your menstrual cycle
🌸 Calculate Your Next Period
Understanding Your Menstrual Cycle
Your menstrual cycle is the monthly process your body goes through to prepare for potential pregnancy. Understanding your cycle helps you predict your period, identify your fertile window, and notice any irregularities that might need attention.
What's "Normal"?
| Aspect | Typical Range | Notes |
|---|---|---|
| Cycle length | 21-35 days | Average is 28 days; yours may differ |
| Period length | 3-7 days | Average is 5 days |
| Blood loss | 30-80ml per cycle | About 2-6 tablespoons total |
| Cycle variation | Up to 7-9 days | Some variation is normal |
The Four Phases
1. Menstruation (Days 1-5): Your period. The uterine lining sheds because pregnancy didn't occur.
2. Follicular Phase (Days 1-13): Overlaps with your period. FSH stimulates follicles in your ovaries; one becomes dominant and matures an egg. Estrogen rises.
3. Ovulation (Day 14): The mature egg is released. This is your most fertile time. The egg survives about 24 hours.
4. Luteal Phase (Days 15-28): The empty follicle becomes the corpus luteum and produces progesterone. If no pregnancy, hormone levels drop and your period begins again.
📊 Day 14 Is Just an Average
Ovulation on day 14 assumes a 28-day cycle. With a 30-day cycle, you'd likely ovulate around day 16. With a 26-day cycle, around day 12. The luteal phase (ovulation to period) is typically consistent at 12-16 days; it's the follicular phase that varies.
Track Your Cycle More Accurately
This calculator gives estimates based on averages. For more accurate tracking, especially if you're TTC, use these methods:
📱 Cycle Tracking Apps
Best free apps:
- Flo — User-friendly, good predictions
- Clue — Science-based, clean design
- Premom — Great for OPK tracking
- Fertility Friend — Gold standard for detailed tracking
🔬 Ovulation Tracking
Easy@Home 50 Ovulation Tests
Detect your LH surge to pinpoint ovulation. More accurate than calendar predictions.
~$16-20
Check Price on Amazon →Clearblue Advanced Digital OPK
Easy digital display—no line interpretation. Detects 4 fertile days.
~$35-45
Check Price on Amazon →When to Be Concerned
While cycle variation is normal, see your doctor if you experience:
- Very irregular cycles (varying by more than 9 days month to month)
- Cycles shorter than 21 days or longer than 35 days consistently
- Periods lasting more than 7 days
- Very heavy bleeding (soaking a pad/tampon every hour)
- Severe pain that interferes with daily activities
- Bleeding between periods
- No period for 3+ months (and you're not pregnant)
These could indicate conditions like PCOS, endometriosis, thyroid issues, or other hormonal imbalances that benefit from treatment.
Frequently Asked Questions
Why is my cycle irregular?
Common causes include stress, weight changes, excessive exercise, PCOS, thyroid disorders, perimenopause, or simply natural variation. If cycles are consistently irregular (varying by more than 9 days), consult your doctor.
Can I get pregnant on my period?
It's unlikely but possible, especially if you have shorter cycles. Sperm can survive 5 days, so if you have sex at the end of your period and ovulate early, conception could occur.
How do I calculate my cycle length?
Count from the first day of one period (day 1 of bleeding) to the day before your next period starts. Track for 3-6 months and calculate the average.
Why is my period late?
Besides pregnancy, periods can be late due to stress, illness, travel, weight changes, excessive exercise, hormonal changes, or certain medications. If your period is more than a week late and you're not pregnant, consult your doctor.