The Menstrual Cycle Calculator helps you track and predict your next period based on your personal cycle pattern.
Enter your last menstrual period (LMP) date, average cycle length, and period duration to get predictions for your next period, estimated ovulation, fertile window, and PMS for the next 3, 6, or 12 months. Includes a color-coded visual calendar, full prediction table, cycle health assessment, and menstrual cycle phase information.
Disclaimer: Predictions are estimates based on average cycle length. Actual cycles can vary. This calculator cannot be used as a contraceptive method.
4 Fase dalam Siklus Menstruasi
🔴
Fase Menstruasi (Hari 1–5)
Lapisan rahim luruh dan keluar sebagai darah haid. Kadar estrogen dan progesteron berada di titik terendah. Berlangsung 2–7 hari.
🟣
Fase Folikuler (Hari 6–13)
Hormon FSH merangsang folikel di ovarium untuk berkembang. Estrogen meningkat, lapisan rahim menebal. Energi dan mood cenderung meningkat.
🟢
Fase Ovulasi (Hari 14)
Lonjakan hormon LH memicu pelepasan sel telur dari ovarium. Ini adalah hari paling subur. Sel telur bertahan 12–24 jam, sperma bisa bertahan 3–5 hari.
🟡
Fase Luteal (Hari 15–28)
Folikel yang pecah berubah menjadi korpus luteum dan menghasilkan progesteron. Jika tidak ada pembuahan, progesteron turun dan siklus dimulai kembali. Gejala PMS muncul di akhir fase ini.
Kapan Harus ke Dokter?
- Siklus secara konsisten lebih pendek dari 21 hari atau lebih panjang dari 35 hari
- Haid berlangsung lebih dari 7 hari atau disertai perdarahan sangat deras
- Nyeri haid sangat hebat hingga mengganggu aktivitas sehari-hari (dismenore berat)
- Tidak haid selama 3 bulan berturut-turut (amenorea) — selain saat hamil
- Perdarahan di luar jadwal haid (perdarahan intermenstrual)
- Perubahan mendadak pada pola siklus yang biasanya teratur
Catatan Penting: Kalkulator ini adalah alat bantu pelacakan dan bersifat estimasi. Prediksi didasarkan pada siklus rata-rata yang Anda masukkan. Siklus nyata bisa bervariasi akibat stres, perubahan berat badan, penyakit, atau faktor hormonal. Kalkulator ini tidak dapat digunakan sebagai metode kontrasepsi. Untuk perencanaan keluarga atau kekhawatiran medis, konsultasikan dengan dokter atau bidan.
Calculator information
📋 How to use this calculator
- Enter the date of your Last Menstrual Period (LMP) - the first day of bleeding, not the last day.
- Enter your average menstrual cycle length in days (normal 21-35 days, default 28).
- Enter your average period duration in days (normal 3-7 days).
- Choose a prediction window: 3, 6, or 12 months ahead for longer-term planning.
- Click Calculate to view a color-coded visual calendar: menstruation (red), fertile window (green), ovulation (yellow), and PMS (purple).
- Use for pregnancy planning, natural family planning, stocking up on supplies, or detecting irregular cycles.
- Track at least 3-6 consecutive cycles for accurate patterns. Consult a doctor if your cycle is consistently under 21 or over 35 days.
🧮 Menstrual Cycle and Ovulation Prediction
Next period = LMP + cycle_length; Ovulation ≈ LMP + (cycle_length - 14); Fertile window = Ovulation - 5 days through Ovulation + 1 day; PMS ≈ 7-10 days before next period
- LMP = first day of the Last Menstrual Period
- cycle_length = number of days from the first day of one period to the first day of the next
- 14 = estimated luteal phase length (relatively constant)
- fertile window = 6-day window with the highest probability of conception
Sperm can survive 3-5 days in the reproductive tract and an egg lives 12-24 hours, giving an effective fertile window of about 6 days.
💡 Worked example: Cycle prediction for a woman with LMP May 1, 2026 and a 28-day cycle
Given:- LMP = May 1, 2026
- Cycle length = 28 days
- Period duration = 5 days
Steps:- May period: May 1-5 (5 days)
- Ovulation = May 1 + (28 - 14) = May 15, 2026
- Fertile window = May 10 (Ovulation -5) through May 16 (Ovulation +1)
- PMS = May 22-28 (7 days before the next period)
- Next period = May 1 + 28 days = May 29, 2026
Result: Fertile window: May 10-16 (highest chance of conception). Next period expected May 29. Note: predictions are estimates only - ovulation can shift due to stress, illness, or hormonal changes.
❓ Frequently asked questions
What is a normal menstrual cycle length?
According to the American College of Obstetricians and Gynecologists (ACOG) and the WHO, a normal menstrual cycle in adult women is 21-35 days, with an average of 28 days. For teens in the first 3 years after menarche, cycles can range more widely (21-45 days). Normal period duration is 2-7 days. Consult a doctor if your cycle is consistently under 21 days, over 35 days, or bleeding lasts longer than 7 days.
How accurate is ovulation prediction?
For a regular 28-day cycle, calendar-based ovulation prediction is reasonably accurate (within ±2 days). Accuracy drops sharply for irregular cycles. For better precision, combine with basal body temperature (BBT) tracking, cervical mucus monitoring, or ovulation predictor kits (LH urine tests). Tracker apps fed consistent data over 6+ months are more accurate than a one-off calculation.
Can pregnancy happen outside the fertile window?
The odds are very low but not zero. Sperm can survive up to 5 days in the fallopian tubes, and ovulation can shift due to stress, illness, weight changes, or travel. Because of this, calendar-based natural family planning has a typical-use failure rate of 12-24% per year, far higher than hormonal contraception (<1%). For reliable pregnancy prevention, use a medical contraceptive method recommended by your clinician.
What causes irregular menstrual cycles?
Common causes include excessive stress, drastic weight changes, extreme exercise, PCOS (polycystic ovary syndrome), thyroid disorders, perimenopause, certain contraceptives, or other medical conditions. In teens, irregular cycles during the first 2-3 years after menarche are usually normal. If irregular cycles come with other symptoms (severe acne, hirsutism, rapid weight gain), see an OB-GYN for hormone evaluation.
What are the phases of the menstrual cycle?
Four phases: (1) Menstruation (days 1-5): shedding of the endometrium. (2) Follicular (days 1-13): ovarian follicles develop and estrogen rises. (3) Ovulation (around day 14): release of the egg, driven by an LH surge. (4) Luteal (days 15-28): the corpus luteum produces progesterone to prepare for pregnancy; without fertilization, progesterone falls and the next period begins. Average total cycle is 28 days.
📚 Sources & references
Last updated: May 11, 2026