🩸 Period Tracker — Free Menstrual Cycle Calculator
Predict your next period, ovulation day and fertile window — private, no login
What Is a Period Tracker?
A period tracker is a tool that helps you record and predict your menstrual cycle. By entering the first day of your last menstrual period (LMP), your average cycle length, and how many days your period typically lasts, the tracker estimates:
- The date of your next period
- Your ovulation day (approximate)
- Your fertile window — the days each cycle when pregnancy is most likely
- A color-coded calendar view of upcoming cycles
Tracking your period is the foundation of women's health awareness. Whether you are trying to conceive, avoiding pregnancy, or simply want to understand your body better, a reliable menstrual cycle calculator gives you actionable insight in seconds.
How the Prediction Works
Our period tracker uses the standard calendar method, the simplest and most widely taught approach to cycle prediction:
- Next period = LMP date + average cycle length (e.g. LMP + 28 days)
- Ovulation day = LMP + (cycle length − 14). For a 28-day cycle this is day 14.
- Fertile window = 5 days before ovulation through 1 day after (sperm survives up to 5 days, the egg up to 24 hours)
This method works best for women whose cycles fall in the normal range of 21–35 days. For irregular cycles, predictions become less reliable — consider combining with ovulation test strips or basal body temperature charting.
What Is a Normal Menstrual Cycle?
Cycle length
Medical consensus (ACOG, Mayo Clinic) defines a normal cycle as 21 to 35 days, with the average around 28 days. Cycles shorter than 21 days (polymenorrhea) or longer than 35 days (oligomenorrhea) may signal hormonal imbalance and warrant a medical review.
Period duration
A typical period lasts 3 to 7 days, with an average of 5 days. Bleeding that lasts longer than 7 days (menorrhagia) or is unusually heavy should be discussed with a healthcare provider.
Flow volume
Total blood loss per period is normally 30–80 ml. Losing more than 80 ml, or needing to change a pad/tampon every hour, may indicate heavy menstrual bleeding.
Common Causes of Irregular Periods
- Stress — cortisol disrupts the hypothalamic-pituitary-ovarian (HPO) axis
- Weight changes — rapid loss or gain, low body fat, or obesity
- Polycystic Ovary Syndrome (PCOS) — a leading cause of oligo-/anovulation
- Thyroid disorders — both hypo- and hyperthyroidism affect cycles
- Perimenopause — cycles shorten, lengthen, or become anovulatory in the years before menopause
- Birth control — starting, stopping, or switching hormonal contraception
- Excessive exercise — the "female athlete triad" of low energy availability, bone loss, and menstrual dysfunction
- Medications — antipsychotics, antidepressants, steroids, and emergency contraception
If your cycles are consistently irregular, missing (amenorrhea), or accompanied by severe pain, please consult a licensed gynecologist.
Benefits of Tracking Your Period
- Fertility awareness — time intercourse for conception or avoid it for natural family planning
- Early detection of cycle changes that may signal health issues
- Pregnancy planning — a tracked LMP is the basis for pregnancy dating and due date calculation
- Symptom correlation — link mood, skin, energy, and pain to cycle phases
- Medical appointments — provide accurate cycle data to your doctor
Frequently Asked Questions
How accurate is the period prediction?
Our period tracker uses the standard calendar method based on your last menstrual period (LMP), cycle length and period duration. For women with regular cycles (21-35 days), predictions are generally reliable. However, individual hormonal fluctuations, stress, diet and medical conditions (such as PCOS or thyroid disorders) may cause variations. The tool is for reference only and not a substitute for medical advice.
Can I use the period tracker with irregular cycles?
Yes, you can still use it, but predictions will be less accurate. Enter your average cycle length over the past 6-12 months. If your cycles vary by more than 7-9 days, consider tracking basal body temperature, ovulation test strips, or consulting a healthcare provider for a personalized assessment.
Is my data stored or sent to a server?
No. All calculations run locally in your browser. We do not collect or upload any personally identifiable information. Your language preference and water tracker count are saved only in your device's local storage.
Can I use this for birth control?
No. The calendar method alone has a high failure rate (typical-use failure ~24% per year). This tool is for awareness and planning, not contraception. For birth control, use a medically validated method and consult a healthcare provider.
Why is my period late but I'm not pregnant?
Late periods have many causes beyond pregnancy: stress, weight changes, intense exercise, thyroid dysfunction, PCOS, perimenopause, medications, and travel/jet lag. If you miss three or more periods (secondary amenorrhea) and have ruled out pregnancy, see a doctor.
Medical Disclaimer
This period tracker is for general reference only and does not constitute medical diagnosis or treatment advice. Calculation results are based on standard formulas and individual physiological differences may affect accuracy. For any health concerns, please consult a licensed physician or other qualified healthcare provider. See our full disclaimer.
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