健康・フィットネス

排卵計算機

生理周期から排卵日と妊娠可能期間を計算

使い方
  1. 最後の生理が始まった日を選択。
  2. 平均生理周期（通常21〜35日）を入力。
  3. Click 妊娠可能期間を計算 to find the days you are most likely to conceive.

計算式

Ovulation typically occurs 14 days before the start of the next menstrual period, regardless of cycle length.

  • The Fertile Window spans from 5 days before ovulation to 1 day after.
  • 精子は女性の生殖管内で最大5日間生存できますが、卵子は排卵後12〜24時間しか生存できません。

免責事項：この計算機は目安を提供するものであり、避妊の主な手段として使用しないでください。

Understanding Your Menstrual Cycle and Ovulation

The menstrual cycle is a complex hormonal process divided into four phases: the menstrual phase (days 1–5), the follicular phase (days 1–13), ovulation (around day 14 in a 28-day cycle), and the luteal phase (days 15–28). Ovulation—the release of a mature egg from the ovarian follicle—is the only time in each cycle when pregnancy is possible.

The timing of ovulation is governed by a surge in Luteinising Hormone (LH), which typically occurs 24–36 hours before the egg is released. Understanding your personal cycle patterns is essential for both family planning and fertility treatment. The Wikipedia article on Ovulation provides a detailed overview of the hormonal cascade and physiological changes involved.

Your Fertile Window: When Is Conception Possible?

While the egg is only viable for 12–24 hours after ovulation, sperm can survive in the female reproductive tract for up to 5 days. This creates the "fertile window"—a 6-day period (5 days before ovulation + ovulation day) during which unprotected intercourse can result in pregnancy.

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Days of highest conception probability:
Day −2 before ovulation: ~27% per cycle
Day −1 before ovulation: ~33% per cycle (peak)
Day 0 (ovulation day): ~33% per cycle
Source: Wilcox AJ et al., NEJM 1995 — the landmark timing-of-conception study.

For couples trying to conceive, timing intercourse in the 2–3 days leading up to and including ovulation maximises the probability of fertilisation. Our calculator uses the standard formula: ovulation occurs 14 days before the next period, regardless of total cycle length.

Signs of Ovulation: How to Know When You’re Fertile

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Basal Body Temperature (BBT) Rise — After ovulation, progesterone causes a sustained temperature rise of 0.2–0.5°C. Tracking BBT with a basal thermometer daily (before getting up) reveals ovulation retrospectively and helps identify your pattern over multiple cycles.
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LH Surge (Ovulation Predictor Kits) — OPK urine tests detect the LH surge 24–36 hours before ovulation. A positive OPK indicates your most fertile days are immediately ahead. Begin testing 3–4 days before your expected ovulation date.
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Cervical Mucus Changes — As ovulation approaches, cervical mucus transitions from thick and white to clear, stretchy, and "egg-white" consistency—the hallmark of peak fertility. This change reflects rising oestrogen levels and facilitates sperm motility.
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Mittelschmerz (Ovulation Pain) — Approximately 20% of women experience mild, one-sided pelvic pain around ovulation. This is caused by follicle rupture and peritoneal fluid leakage. While not universally reliable, it can serve as a supplementary fertility sign.

Maximising Fertility: Evidence-Based Tips for Conception

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Folic Acid Supplementation — 400–800 mcg/day before and during early pregnancy significantly reduces neural tube defect risk. The American College of Obstetricians and Gynecologists (ACOG) recommends starting at least one month before attempting conception.
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Maintain a Healthy BMI — Both underweight (BMI <18.5) and obesity (BMI >30) impair ovulation. Women with PCOS particularly benefit from moderate weight loss to restore cycle regularity and ovulatory function.
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Avoid Smoking, Alcohol & Excessive Caffeine — Smoking accelerates ovarian ageing. Alcohol intake above 2 drinks/week is associated with reduced fertility. Caffeine above 200–300 mg/day may modestly impact conception rates.
🤼
Regular Moderate Exercise — 30–60 minutes of moderate activity daily supports hormonal balance and a healthy BMI. However, extreme high-intensity exercise can suppress ovulation through hypothalamic dysfunction.

Frequently Asked Questions About Ovulation

生理中に妊娠する可能性はありますか？

Very unlikely, but theoretically possible in women with short cycles (21–24 days). If ovulation occurs unusually early (around day 7–8) and sperm survive 5 days from late-period intercourse, conception could occur. This is rare but not impossible. Most menstrual cycles have a low-fertility window during menstruation itself.

排卵計算機はどれほど信頼できますか？

Calendar-based calculators are most reliable for women with very regular cycles. Research shows that ovulation timing varies significantly even in women who believe their cycles are regular—only about 30% of women have their fertile window fall within the assumed "days 10–17" period. For higher accuracy, combine calendar tracking with OPK testing and BBT charting.

不妊専門医にはいつ相談すべきですか？

If you are under 35 and have been trying to conceive for 12 months without success, or over 35 and trying for 6 months, ACOG recommends consulting a reproductive endocrinologist or fertility specialist. Women with known conditions like PCOS, endometriosis, or irregular cycles should seek evaluation sooner.

Related Health Calculators

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妊娠計算機Due date, gestational age & trimester milestones
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BMI計算機Healthy weight assessment before conception
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カロリー計算機Nutritional needs planning for pregnancy
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理想体重計算機Pre-pregnancy weight range by height

References & Further Reading

  1. Wilcox AJ, et al. Timing of sexual intercourse in relation to ovulation. NEJM, 1995.
  2. Wikipedia contributors. Ovulation. Wikipedia, The Free Encyclopedia.
  3. Wikipedia contributors. Menstrual Cycle. Wikipedia, The Free Encyclopedia.
  4. ACOG. Fertility Awareness-Based Methods of Family Planning. American College of Obstetricians and Gynecologists, 2023.
  5. NHS. How long does it take to get pregnant?. NHS, 2023.