Menstrual Cycle Calculator: Next Period, Ovulation & Fertile Window
Menstrual Cycle Calculator
Knowing your cycle helps with health management, travel planning, and pregnancy preparation. Enter your last period start date and your average cycle length.
Menstrual Cycle Calculator
Predict your next period, ovulation & fertile window
Today is — Day 15 of cycle
Fertile
August 1, 2026
~ August 5, 2026
14 days away
July 18, 2026
Today
July 13, 2026
~ July 18, 2026
5 days ago
July 19, 2026
~ August 1, 2026
1 days away
Cycle Phases
Next 3 Cycles Forecast
🩸
Aug 29
🥚
Aug 15
💕
Aug 10 ~
🩸
Sep 26
🥚
Sep 12
💕
Sep 7 ~
🩸
Oct 24
🥚
Oct 10
💕
Oct 5 ~
💡 Health Tips
- •A normal menstrual cycle ranges from 21 to 35 days.
- •Ovulation typically occurs around day 14 of the cycle, but varies per person.
- •The fertile window spans from 5 days before ovulation to ovulation day itself.
- •If your cycle is irregular or painful, consult a healthcare professional.
This calculator assumes a typical cycle. Do not use it for medical purposes.
Cycle Basics
Average cycle: 21–35 days (average 28 days)
Period duration: 3–7 days
Ovulation: approximately 14 days before the next expected period
| Phase | Days (28-day cycle) | Key Features |
|---|---|---|
| Menstruation | Days 1–5 | Uterine lining sheds, hormones at lowest |
| Follicular | Days 6–13 | Rising estrogen, increasing energy |
| Ovulation | Around day 14 | Fertility peak, LH surge |
| Luteal | Days 15–28 | Rising progesterone, PMS may begin |
Fertile window: Approx. 5 days before ovulation + ovulation day + 1 day after = ~7 days total. Sperm can survive 3–5 days in the body, so the window begins before the ovulation day.
Irregular Cycle Reference
| Condition | Definition |
|---|---|
| Normal range | Cycle 21–35 days, variation ±7 days |
| Frequent periods | Cycle under 21 days |
| Infrequent periods | Cycle over 35 days |
| Amenorrhea | No period for 3+ months |
| Heavy bleeding | Excessive flow (soaking a pad within an hour) |
This calculator provides average-cycle-based estimates. Stress, weight changes, and hormonal imbalances can shift actual ovulation. If you are trying to conceive or need contraception, combine this with an ovulation test and consult a gynecologist.
PMS (Premenstrual Syndrome) Management
PMS commonly occurs in the luteal phase (days 15–28) after ovulation.
- Physical symptoms: Breast tenderness, bloating, headaches, fatigue
- Emotional symptoms: Irritability, low mood, difficulty concentrating
- Management: Regular aerobic exercise, reducing caffeine/sodium intake, adequate sleep, magnesium supplementation
OIYO Editorial
Editorial DeskThe OIYO editorial desk researches money, law, lifestyle, and self-understanding topics against primary sources and public statistics. Every piece carries source notes and is reviewed on a regular cycle for accuracy and usefulness.